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&M S E 9 1 E S F n D E 8 I 6 Rt E N S I N E £ B « 

' THE ART AND SCIENCE OF 

Analog Circuit Design 



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EDITED BY Jim Williams 



The Art and Science of 
Analog Circuit Design 



The EDN Series for Design Engineers 



J.Williams 
]. Lenk 

V. Lakshminarayanan 
J . Lenk 

M. Brown 

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R. Marston 

N. Dye and H. Granberg 

Gates Energy Products 

T. Williams 
J.Williams 

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The Art and Science of Analog Circuit 
Design 

Simplified Design of Switching Power 
Supplies 

Electronic Circuit Design Ideas 
Simplified Design of Linear Power 
Supplies 

Power Supply Cookbook 
EDN Designer's Companion 
Operational Amplifiers, Second Edition 
Circuit Designer's Companion 
Electronics Circuits Pocket Book: Passive 
and Discrete Circuits (Vol. 2) 
Radio Frequency Transistors: Principles 
and Practical Applications 
Rechargeable Batteries: Applications 
Handbook 

EMC for Product Designers 

Analog Circuit Design: Art, Science, and 

Personalities 

Troubleshooting Analog Circuits 
Electronic Circuits, Systems and Standards 
Electronic Circuits Pocket Book: Linear 
ICs(VoLl) 

Integrated Circuit and Waveform 

Generator Handbook 

Passive Components: A User's Guide 



The Art 
and Science of 

Analog 
Circuit Design 



Edited by 

Jim Williams 



Butterworth-Heinemann 

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MIT building 20 at 3:00 A.M. 
Tek. 547, pizza, breadboard. 
That's Education. 



This page intentionally left blank 



Contents 



Preface ix 
Contributors xi 

Part One Learning How 



1 . The Importance of Fixing 3 

Jim Williams 

2. How to Grow Strong, Healthy Engineers 9 

Barry Harvey 

3. We Used to Get Burned a Lot, and We Liked It 1 7 

Barry Harvey 

4. Analog Design Productivity and the Challenge 

of Greatir^ Future Generations of Analog Engineers 31 

Keitaro Sekine 

5. Thoughts on Becoming and Being an Analog 
Circuit Designer 41 

Gregory T. A. Kovacs 

6. Cargo Cult Science 55 

Richard P, Feynman 



Part f^ Raking It Work 



7. 


Signat Conditioning in Oscilloscopes and the 




Spirit of Invention 65 




Steve Roach 


8. 


One Trip Down the IC Development Road 85 




William H. Gross 


9. 


Analog Breadboarding 103 




James M. Bryant 


10. 


Who Wakes the Bugler? 121 




Carl Battjes 


11. 


Tripping ttre Light Fantastic 1 39 




Jim Williams 



vii 



Part Three Sellmglt 



1 2. Analog Circuit Design for Fun and Profit 1 97 

Doug Grant 

1 3. A New Graduate^s Guide to the Analog Interview 21 9 

Robert Reay 

1 4. John Harrison's "Ticking Box" 233 

Lloyd Brown 

Part Four Guidance and Commentary 



15. Moore's Law 251 

Eric Swanson 

1 6. Analog Circuit Design 263 

John Willison 

1 7. There's No Place Like Home 269 

Jim Williams 

1 8. It Starts with Tomorrow 279 

Barrie Gilbert 

1 9. The Art and Science of Linear IC Design 327 

Carl Nelson 

20. Analog Design— Thought Process, Ba§ of 
Tricks, Trial and Error, or Dumb Luck? 343 

Arthur D. Delagrange 



Index 



391 



Preface 



This book continues the approach originated in an earlier effort, "Analog 
Circuit Design — Art, Science, and Personalities." In that book twenty-six 
authors presented tutorial, historical, and editorial viewpoints on subjects 
related to analog circuit design. The book encouraged readers to develop 
their own approach to design. It attempted this by presenting the diver- 
gent methods and views of people who had achieved some measure of 
success in the field. A complete statement of this approach was contained 
in the first book's preface, which is reprinted here (immediately follow- 
ing) for convenience. 

The surprisingly enthusiastic response to the first book has resulted in 
this second effort. This book is similar in spirit, but some changes have 
occurred- The most obvious difference is that almost all contributors are 
new recruits. This seems a reasonable choice: new authors with new 
things to say, hopefully augmenting the first book's message. 

Alth€ffljgh accomplished, some of this book's writers are significantly 
younger and have less experience at analog design than the previous 
book's authors. This is deliberate, and an attempt to maintain a balanced 
and divergent forum unencumbered by an aging priesthood. 

A final difference is the heavy capitalistic and marketeering influence 
in many of the chapters. This unplanned emphasis is at center stage in 
sections by Grant, Williams, Brown, and others, and appears in most 
chapters. The influence of economics was present in parts of the earlier 
book, but is much more pronounced here. The pristine pursuit of circuit 
design is tempered by economic realities, and the role of money as de- 
sign motivator and modulator is undeniable. 

We hope this book is as well received as the earlier effort, even as it 
broadens the scope of topics and utilizes new authors. As before, it was 
fun to put together. If we have done our job, it should be rewarding for 
the reeder. 

l^f^^M^^ and 
Persofiatittes" 

This is a weird book. When I was asked to write it I refused, because I 
didn't believe anybody could, or should, try to explain how to do analog 
design. Later, I decided the book might be possible, but only if it was 
written by many authors, all with their own styles, topics, and opinions. 



ix 



There should be an absolute minimum of editing, no subject or style re- 
quirements, no planned page count, no outline, no nothing! I wanted the 
book's construction to reflect its subject. What I asked for was essentially 
a mandate for chaos. To my utter astonishment the publisher agreed and 
we lurched hopefully forward. 

A meeting at my home in Fetmiary 1989 was well attended by poten- 
tial participants. What we concluded went something like this: everyone 
would go off and write about anything that could remotely be construed 
as relevant to analog design. Additionally, no author would tell miy other 
author what they were writing about. The hc^ was that the rj^^ would 
see many different styles and approaches to analog design, along with 
some conuiionalities. Hopefully, this would lend courage to someone 
seeking to do analog woric. There are many very different ways to pro- 
ceed, and every designer has to find a way that feels right. 

This evolution of a style, of getting to know oneself, is critical to 
doing good design. The single greatest asset a designer has is self- 
knowledge. Knowing when your thinking feels right* md when you're 
trying to fool yourself. Recognizing when the design is where you want it 
to be, and when you're pretending it is because you're only human. 
Knowing your strengths and weaknesses, prowesses and preiudices. 
Learning to recognize when to ask questions and when to believe your 
answers. 

Formal training can augment all this, but cannot replace it or obviate 
its necessity. I think that factor is responsible for some of the mystique 
associated with analog design. Further, I think that someone approaching 
the field needs to see that there are lots of ways to do this stuff. They 
should be made to feel comfortable experimenting and evolving their 
own methods. 

The risk in this book, that it will come across as an exercise in discord, 
is also its promise. As it went together, I began to feel less nervous. 
People wrote about all kinds of things in all kinds of ways. They had 
some very different views of the world. But also detectable were com- 
monalities many found essential. It is our hope that readers will see this 
somewhat discordant book as a reflection of the analog design process. 
Take what you like, cook it any way you want to, and leave the rest. 

Things wouldn't be complete without a special thanks to Carol Lewis 
and Harry Helms at High Text Publications, and John Martindale at 
Butterworth-Heinemann Publishers. They took on a book with an amor- 
phous charter and no rudder and made it work. A midstream change of 
publishers didn't bother Carol and Harry, and John didn't seem to get 
nervous over a pretty risky approach to book writing. 

I hope this book is as interesting and fun to read as it was to put to- 
gether. Have a good time. 



Contributors 



Jm Williams is the editor-in-chief of this second volume on analog 
circuit design. As with the first volume, Jim developed the basic concept 
of the book, identified, contacted, and cajoled potential contributors, and 
edited the contributions. Jim was at the Massachusetts Institute of Tech- 
nology from 1968 to 1979, concentrating exclusively on analog circuit 
design. His teaching and research interests involved application of analog 
circuit techniques to biochemical and biomedical problems. Concur- 
rently, he consulted U.S. and foreign concerns and governments, special- 
izing in analog circuits. In 1979, he moved to National Semiconductor 
Corporation, continuing his work in the analog area with the Linear Inte- 
grated Circuits Group. In 1982 he joined Linear Technology Corporation 
as staff scientist, where he is presently employed. Interests include prod- 
uct definition, development, and support. Jim has authored over 250 pub- 
lications relating to analog circuit design. He received the 1992 Innovator 
of the Year Award from EDN Magazine for work in high-speed circuits. 
His spare tiim interests include sports cars, collecting antique scientific 
instruments, art, and restoring and using old Tektronix oscilloscopes. 
He lives in Palo Alto, California with his son Michael, a dog named 
Bonillas, and 28 Tektronix oscilloscopes. 

Carl Battjes has worked in the analog design of systems with a focus 
on detailed design at the bipolar transistor device and bipolar IC level. 
He has been involved in the design of Tektronix, Inc. oscilloscopes and 
their components, such as delay lines, filters, attenuators, and amplifiers. 
For the Grass Valley Group, he developed a precision analog multiplier 
for video effects. Carl has been a consultant for over ten years and has 
done major detailed designs for the Tektronix 1 1 A72 pre-amp IC, Seiko 
message watch receiver IC, and IC for King Radio (Allied Signal) re- 
ceiver. A registered Professional Engineer in Oregon who holds seven 
patents, he has a BSEE from the University of Michigan and an MSEE 
from Stanford University. 

James Bryant is head of European applications at Analog Devices. He 
lives in England and is a Eur. Ing. and MIEE and has degrees in philoso- 
phy and physics from the University of Leeds. He has over twenty years' 
experience as an analog and RF applications engineer and is well loiown 
as a lecturer and author. His other interests include archery, cooking, ham 
radio (G4CLF), hypnotism, literature, music, and travel. 



xi 



Art Delagrange, when he was young, took his electric train apart and 
reassembled it by himself. Since that day, it has not run. He attended 
MIT, where he studied digital circuitry, receiving a BS/MS in electrical 
engineering in 1961/62. During his graduate year he worked on a hybrid 
digital/analog computer. It did not revolutionize the industry. Beginning 
as a co-op student, he worked for 33 years for the Naval Surf ace Warfare 
Center in Silver Spring, Maryland. Among his other achievements are a 
PhD in electrical engineering from the University of Maryland, ten 
patents, and 23 articles in the open literature. Retired from the govern- 
ment, he works for Applied Technology and Research in Burtonsvifle, 
Maryland. Art lives in Mt. Airy, Maryland, with his wife, Janice, and his 
cat. Clumsy. His hobbies are cars, boats, sports, music, and opening 
packages from the wrong end. 

Richard P. Feynman was professor of physics at the California Institute 
of Technology. He was educated at MIT and Princeton, and worked on 
the Manhattan Project during World War II. He received the 1965 Nobel 
Prize in Physics for work in quantum electrodynamics. His life and style 
have been the subject of numerous biographies. He was an uncommonly 
good problem solver, with notable ability to reduce seemingly complex 
issues to relatively simple terms. His Feynman Lectures on F/iy^ic^, pub- 
lished in the 60s, are considered authoritative classics. He died in 1988. 

Barrie Gilbert has spent most of his life designing analog circuits, 
beginning with four-pin vacuum tubes in the late 1940s. Work on speech 
encoding and synthesis at the Signals Research and Development Estab- 
lishment in Britain began a love affair with the bipolar transistor that 
shows no signs of cooling off. Barrie joined Analog Devices in 1972, 
where he is now a Division Fellow working on a wide variety of IC prod- 
ucts and processes while managing the Northwest Labs in Beaverton, 
Oregon. He has published over 40 technical papers and been awarded 20 
patents, Barrie received The IEEE Outstanding Achievement Award in 
1970, was named an IEEE Fellow in 1984, and received the IEEE Solid- 
State Circuits Council Outstanding Development Award in 1986; For 
recreation, Barrie used to climb mountains, but nowadays stays home and 
tries to write music in a classical style for performance on a cluster of 
eight computer-controlled synthesizers and other toys. 

Doug Grant received a BSEE degree from the Lowell Technological 
Institute (now University of Massachusetts-Lowell) in 1975. He joined 
Analog Devices in 1976 as a design engineer and has held several positions 
in engineering and marketing prior to his current position as marketing 
manager for RF products. He has authored numerous papers and articles on 
mixed-signal and linear circuits, as well as his amateur radio hobby. 

Bill Gross is a design manager for Linear Technology Corporation, 
heading a team of design engineers developing references, precision 



amplifiers, high-speed amplifiers, comparators, and other high-speed 
products. Mr. Gross has been designing integrated circuits for the semi- 
conductor indtistry for 20 years, first at National Semiconductor, includ- 
ing three years living and working in Japan, and later at Elantec. He has a 
BSEE from California State Polytechnic University at Pomona and an 
MSEE from the University of Arizona at Tucson, He is married and the 
father of two teenage sons, whose sports activities keep him quite busy. 

Barey Harvey is a designer of bipolar analog integrated circuits at 
Elantec, Inc. His first electronic projects were dismantling vacuum tube 
television sets as a child and later in life rebuilding them. These days he 
tortures silicon under a microscope. 

Gregory T.A. Kovacs received a BASc degree in electrical engineering 
from the University of British Columbia, Vancouver, British Columbia, 
in 1984; an MS degree in bioengineering from the University of Cali- 
fornia, Berkeley, in 1985; a PhD degree in electrical engineering from 
Stanford University in 1990; and an MD degree from Stanford University 
in 1992. His industry experience includes the design of a wide variety of 
analog and mixed-signal circuits for industrial and commercial applica- 
tions, patent law consulting, and the co-founding of three electronics 
companies. In 1991, he joined Stanford University as Assistant Professor 
of Electronic Engineering, where he teaches analog circuit design and 
micromaehined transducer technologies. He holds the Robert N. Noyce 
Family Faculty Scholar Chair, received an NSF Young Investigator 
Award in 1993, and was appointed a Terman Fellow in 1994. His present 
research areas include neural/electronic interfaces, solid-state sensors and 
actuators, micromaehining, analog circuits, integrated circuit fabrica- 
tions, medical instruments, and biotechnology. 

Cari. Nelson is Linear Technology's Bipolar Design Manager. He has 
25 years in the semiconductor IC industry. Carl joined Linear Technology 
shortly after the company was founded. He came from National Semicon- 
ductor and before that worked for Teledyne Semiconductor. He has a 
BSEE from the Northrup Institute of Technology. He is the designer of 
the first temperature-sensor IC and is the father of the LT1070/1270 fam- 
ily of easy-to-use switching regulators. He holds more than 30 patents on 
a wide range of analog integrated circuits. 

Robert Reay became an analog designer after discovering as a teenager 
that the manual for his Radio Shack electronics kit didn't describe how 
any of the circuits really worked. His scientific curiosity and realization 
that he wasn't going to make any money as a pianist led him to Stanford 
University, where he earned his BSEE and MSEE in 1984. He worked 
for Intersil, designing data conversion products, for four years before 
Maxim hired away most of the design team. He is currently managing a 
group of designers at Linear Technology Corporation, doing interface 



circuits, battery chargers, DACs, references, comparators, regulators, 
temperature sensors, and anything else ttiat looks interesting. He regu- 
larly plays roller blade hockey with the kids in the neighborhood and is 
helping his children discover the beauty of a Chopin waltz and a well- 
designed circuit. 

Steve Roach received his BS in engineering physics from the Univer- 
sity of Colorado in 1984 and his MS in electrical engineering from Ohio 
State University in 1988. He worked from 1984 to 1986 as a software 
engineer for Burroughs Corporation and from 1988 to 1992 at Hewlett- 
Packard Company, designing digital oscilloscopes. From 1992 to 1994, 
Stephen designed industrial sensors at Kaman Instrumentation Company. 
He is currently designing digital oscilloscopes for Hewlett-Packard. His 
hobbies include backpacking, hunting, off-road motorcycling, and tutor- 
ing kids at the Boys* and Girls' Club. 

Keitaro Serine received his BE, ME, and Dr. Eng. degrees in electron- 
ics from Waseda University in 1960, 1962, and 1968, respectively. Since 
1969, he has been with the Faculty of Science and Technology, Science 
University of Tokyo, where he is now a professor in the Department of 
Electrical Engineering. His main research interests are in analog inte- 
grated circuits and their application systems. His interests in the physical 
aspects of analog circuits, such as implementation, mutual electro-mag- 
netic couple within the circuits, and EMC, originated from the experi- 
ments at his own amateur radio station, which he has had since 1957 . He 
has been chair of the Committee for Investigative Research and Commit- 
tee on Analog Circuit Design Technologies at the Institute of Eleotrical 
Engineers of Japan (lEEJ) and also a member of the Editorial Committee 
for the Transactions of lEICE Section J-C. He is now president of the 
Society for Electronics, Information, and System at the lEEJ, as well as a 
member of the Board of Directors at the Japan Institute of Printed Circuit 
(JIPC). Dr. Sekine is a member of the Institute of Electrical and 
Electronics Engineers, the lEEJ, and the JIPC. 

Eric Swanson received his BSEE from Michigan State University in 
1977 and his MSEE from Cal Tech in 1980. From 1980 to 1985 he 
worked on a variety of analog LSI circuits at AT&T-Bell Laboratories in 
Reading, Pennsylvania. In 1985 he joined Crystal Semiconductor in 
Austin, Texas, where he is currently Vice President of Technology. His 
development experience includes millions of CMOS transistors, a few 
dozen bipolar transistors, and nary a vacuum tube. Eric holds 20 patents, 
evenly divided between the analog and digital domains, and continues to 
design high-performance data converters. He enjoys swimming and bik- 
ing with his wife Carol and four children. 



John Willison is the founder of Stanford Research Systems and the 
Director of R&D. Considered a renegade for having left "pure research" 
after completing a PhD in atomic physics, he continues to enjoy design- 
ing electronic instruments in northern California. Married with four chil- 
dren, he's in about as deep as you can get. 



This page intentionally left blank 



Part One 



Learning How 



The book's initial chapters present various methods for learning how to 
do analog design. Jim Williams describes the most efficient educational 
mechanism he has encountered in "The Importance of Fixing." A pair of 
chapters from Barry Harvey emphasize the importance of realistic expe- 
rience and just how to train analog designers. Keitaro Sekine looks at 
where future Japanese analog designers will come from. He has particu- 
larly pungent commentary on the effects of "computer-based" design on 
today's students. Similar concerns come from Stanford University pro- 
fessor Greg Ko vacs, who adds colorful descriptions of the nature of ana- 
log design and its practitioners. Finally, Nobel prize-winning physicist 
Richard P. Feynman's 1974 Cal Tech commencement address is pre- 
sented. Although Feynman wasn't an analog circuit designer, his obser- 
vations are exceptionally pertinent to anyone trying to think clearly about 
anything. 



1 



This page intentionally left blank 



JimWHriams 

1. The Importance of Fixing 



Fall 1968 found me at MIT preparing courses, negotiating thesis topics 
with students, and getting my laboratory together. Hiis was fairly unre- 
markable behavior for this locale, but for a 20 year old college dropout 
the circumstances were charged; the one chance at any sort of career. For 
reasons I'll never understand, my education, from kindergarten to col- 
lege, had been a nightmare, perhaps the greatest impedance mismatch in 
history, I got hot. The Detroit Board of Education didn't. Leaving Wayne 
State University after a dismal year and a half seemed to close the casket 
on my circuit design dreams. 

AH this history conspired to give me an outlook blended of terror and 
excitement. But mostly terror. Here I was, back in school, but on the 
other side of the lectern. Worse yet, my research project, while of my 
own choosing, seemed open ended and unattainable. I was so scjured I 
couldn't breathe out. The capper was my social situation. I was younger 
than some of my students, and my colleagues were at least 10 years past 
me. To call things awkward is the gentlest of verbiage. 

The architect of this odd brew of affairs was Jerrold R. Zacharias, 
eminent physicist, Manhattan Project and Radiation Lab alumnus, and 
father of atomic time. It was Jerrold who wav<^ a magic wand and got 
me an MIT appointment, and Jerrold who hmid^me carte blanche a lab 
and operating money. It was also Jerrold who made it quite clear that he 
expected results. Jerrold was not the sort to tolerate looking foolish, and 
to fail him promised a far worse fate than dropping out of school. 

Against this background I received my laboratory budget request back 
from review. The utter, untrammeled freedom he permitted me was main- 
tained. There were no quibbles. Everything I requested, even very costly 
items, was approved, without comment or question. The sole deviation 
from this I found annoying. He threw out my allocation for instrument 
repair and calibration. His hand written comment: "You fix everything." 

It didn't make sense. Here I was, luider pressure for results, scared to 
pieces, and I was supposed to waste time scmwing around fixing lab 
equipment? I went to see Jerrold. I asked. I negotiated. I pleaded, I 
ranted, and I lost. The last thing I heard chasing me out of his office was, 
**¥bu fix every thing." 

I couldn't know it, but this was my introduction to the next ten years. 
An unruly mix of airy freedom and tough intellectual discipline that 



3 



The Importance of Fixing 



would seemingly be unremittingly pounded into me. No apprenticeship 
was ever more necessary, better delivered, or, years later, as appreciated. 

I cooled off, and the issue seemed irrelevant, because nothing broke 
for a while* The first thing to finally die was a high sensitivity, differen- 
tial *scope plug-in, a Tektronix 1 A7. Life would never be the same. 

The problem wasn't particularly difficult to find once I took the time 
to understand how the thing worked. The manual's level of detail and 
writing tone were notable; communication was the priority. This seemed 
a significant variance from academic publications, and I was impressed. 
The instrument more than justified the manual's efforts. It was gorgeous. 
The integration of mechanicals, layout, and electronics was like nothing I 
had ever seen. Hours after the thing was fixed I continued to probe and 
puzzle through its subtleties. A common mode bootstrap scheme was 
particularly interesting; it had direct applicability to my lab work. 
Similarly, I resolved to wholesale steal the techniques used for reducing 
input current and noise. 

Over the next month 1 found myself continually drifting away from 
my lesearch project, taking apart test equipment to see how it worked- 
This was interesting in itself* but what I really wanted was to test my 




Figure 1-1. 

on boy, if s 
broken! Life doesn't 
get any better than 

this. 



understanding by having to fix it. Unfortunately, Tektronix, Hewlett- 
Packard, Fluke, and the rest of that ilk had done their work well; the stuff 
didn't break. I offered free repair services to other labs who would bring 
me instruments to fix. Not too naany takers. People had repak budgets . . . 
and were unwilling to risk their equipn:^t to my unproven care. Finally, 
in desperation, Ipaid people (in standard MIT currency— Coke and 
pixza) to cteiajerately disable my test equipment so I could fix it. Now, 
their only possible risk was indigestion. This offer worked well. 

A few of my students became similarly hooked and we engaged in all 
forms of contesting. After a while the "breakers" developed an antiada of 
incredibly arcMe diseases to visit on the instruments. The "fixers" coun- 
tered with ever more sophisticated analysis capabilities. Various games 
took points off for every test connection made to an instrument's innards, 
the em^asis being on how close you could get utilizing panel controls 
and connectors. Fixing without a schematic was highly regarded, and a 
consummately macho test of analytical skill and circuit sense. Still other 
versions rewarded pure speed of repair, irrespective of method.^ It really 
was great fun. It was also highly efficient, serious education. 

The inside of a broken, but well-designed piece of test equipment is an 
extraordinarily effective classroom. The age or purpose of the instrument 
is a minor concern. Its instructive value derives from several perspectives. 

It is always worthwhile to look at how the designer(s) dealt with prob- 
lems, utilizing available technology, and within the constraints of cost, 
size, power, and other realities. Whether the instrument is three months 
or thirty years old has no bearing on the quality of the thinking that went 
into it. Good design is independent of technology and basically timeless. 
The clever, elegant, and often interdisciplinary approaches found in many 
instruments are eye-opening, and frequently directly applicable to your 
own design work. More importantly, they force self-examination, hope- 
fully preventing rote approaches to problem solving, with their attendant 
mediocre results. The specific circuit tricks you see are certainly adapt- 
able and useful, but not nearly as valuable as studying the thought 
process that produced them. 

The fact that the instrument is broken provides a unique opportunity. A 
br<Aen instrument (or anything else) is a capsulized mystery, a puzzle 
with a definite and very singular "right" answer. The one true reason why 
that instrument doesn't work as it was intended to is really there. You are 
forced to measure your performance against an absolute, non-negotiable 
standard; the thing either works or it doesn't when you're finished. 



I. A more recent development is "phone fixing " This team exercise, derived by Len Sherman (the 
most adept fixer i know) and the author, places a telephone-equipped person at the bench with 
the brokeatt instrument. Hie paitner, someWtoe else, has the schematic aiid a tetephone. The two 
work tegedi^ to make the fix. A surprise is that the llme'-to-fix seems to be kss dm if both 
parties are physicaliy together. This may be due to dilation of ego factors. Both partners simply 
must speak and listen with exquisite care to get the thing fixed. 



Tlie Importance of Fixing 



The reason all this is so valuable is that it brutally tests your thinking 
process. Fast judgments, glitzy explanations, and specious, hand-waving 
arguments cannot be costumed as "creative" activity or true understand- 
ing of the problem. After each ego-inspired lunge or jumped conclusion, 
you confront the uncompromising reality that the damn thing still doesn't 
work. The utter closedness of the intellectual system prevents you from 
fooling yourself. When it's finally over, and the box works, and you 
know why, then the real work begins. You get to try and fix you. The bad 
conclusions, poor technique, failed explanations, and crummy arguments 
all demand review. It's an embarrassing process, but quite vahmWe, Yoti 
learn to dance with problems, instead of trying to mug them. 

It's scary to wonder how much of this sort of sloppy thinking slips into 
your own design work. In that arena, the system is not closed. There is no 
arbitrarily right answer, only choices. Things can work, but not as well as 
they might if your thinking had been better. In the worst case, things 
work, but for different reasons than you think. That's a disaster, and more 
conunon than might be supposed. For me, the most dangerous point in a 
design comes when it "works." This ostensibly "proves" that my thinking 
is correct, which is certainly not necessarily true. The luxury the broken 
instrument's closed intellectual system provides is no longer avaifeble. In 
design work, results are open to interpretation and explanation and that's 
a very dangerous time. When a design "works" is a very delicate stage: 
you are psychologically ready for the kill and less inclined to continue 
testing your results and thinking. That's a precarious place to be, and you 
have to be so careful not to get into trouble. The very humanness that 
drives you to solve the problem can betray you near the finish line. 

What all this means is that fixing things is excellent exercise for doing 
design work. A sort of bicycle with training wheels that prevent you from 
getting into too much trouble. In design work you have to mix a willing- 
ness to try anything with what you hope is critical thinking. This seem- 
ingly immiscible combination can lead you to a lot of nowheres. The 
broken instmment's narrow, insistent test of your thinking isn't there, and 
you can get in a lot deeper before you realize you blew it. The embarrass- 
ing lessons you're forced to learn when fixing instruments hopefully 
prevent this. This is the major reason I've been addicted to fixing since 
1968. I'm fairly sure it was also Jerrold's reason for bouncing my instru- 
ment repair allocation. 

There are, of course, less lofty adjunct benefits to fixing. You can often 
buy broken equipment at absurdly low cost. I once paid ten bucks for a 
dead Tektronix 454A 1 50MHz portable oscilloscope. It had clearly been 
systematically sabotaged by some weekend-bound calibration technician 
and tagged "Beyond Repair." This machine required thirty hours to un- 
cover the various nasty tricks played in its bowels to ensure that it was 
scrapped. 

TTiis kind of devotion highlights another, secondary beneik of fixing. 
There is a certain satisfaction, a kind of service to a moral inaperative, 



6 



that comes from restoring a high-quality instrument. This is unquestion- 
ably a gooey, hand-over-the-heart judgment, and I confess a long-term 
love affair with instrumentation. It just seems sacrilege to let a good 
piece of equipment die. Finally, fixing is simply a lot of fun, I may be 
the only person at an electronics flea market who will pay more for the 
busted stuff! 



This page intentionally left blank 



Barry Harvey 



2. How to Grow Strong, Healthy Engineers 



Graduating engineering students have a rough time of it lately. Used to 
be, most grads were employable and could be hired for many jobs. Ten 
years ago and earlier, there were a lot of jobs. Now, there aren't so many 
and employers demand relevant course work for the myriad of esoteric 
pursuits in electrical engineering. Of those grads that do get hired, the 
majority fail in their first professional placement. 

We should wonder, is this an unhealthy industry for young engineers? 
Well, I guess so. Although I am productive and comfortable now, I was 
not successful in my first three jobs, encompassing nine years of profes- 
sional waste. Although I designed several analog ICs that worked in this 
period, none made it to market. 

Let me define what I call professional success: 

The successful engineer delivers to his or her employer at least 2M 
times the yearly salary in directly attributable sales or efficiency. It may 
take years to assess this. 

For many positions, it's easy to take this measure. For others, such as 
in quality assurance, one assays the damage done to the company for not 
executing one's duties. This is more nebulous and requires a wider busi- 
ness acumen to make the measure. At this point, let me pose what I think 
is the central function of the engineer: 

Engineers create, support, and sell machines. 

That's our purpose. A microprocessor is a machine; so is a hammer or 
a glove. rU call anything which extends human ability a machine. 

It doesn't stop with the designer: the manufacturing workers and engi- 
neers really make the machines, long-term. There's lots of engineering 
support, and all for making the machines and encouraging our beloved 
customers to buy them. Some people don't understand or savor this defi- 
nition, but it's been the role of engineers since the beginning of the in- 
dustrial revolution. I personally like it. I like the structure of business, the 
creation of products, the manufacture of them, and the publicizing of 
them. Our products are like our children, maybe more like our pets. They 
have lives, some healthy and some sickly. Four of my ICs have healthy, 
popular lives; ten are doing just OK; and six are just not popular in the 
market. Others have died. 

A young engineering student won't ever hear of this in school. Our 
colleges' faculties are uneasy with the engineers' charter. The students 



9 



How to Grow Strong, Healthy Engineers 



don't know that they will be held to standards of productivity. They are 
taught that engiiieering is like science, sort of. But science need not pro- 
vide econoniic virtue; engineering pursuits must. 

So what is the state of engineering for the new grad? Mixed. Hope- 
fully, the grad will initially be given procedural tasks that will be suc- 
cessful and lead to more independent projects. At worst, as in my 
experience, the young engineer will be assigned to projects better left to 
seasoned engineers. These projects generally veer off on some strange 
trajectory, and those involved suffer. Oddly enough, the young engineer 
receives the same raises per year for each possibility. After all, the young 
engineer is nothing but "potential'* in the company's view. 

What, then, is the initial value of a young engineer? The ability to 
support ongoing duties in a company? Not usually; sustaining engineer- 
ing requires specific training not available in college, and ]^ssMy not 
transferable between similar companies. Design ability due to new topics 
available in academia? Probably not, for two reasons. First, colleges typi- 
cally follow rather than lead progress in industry. Second, new grads 
can' t seem to design their way out of a paper bag, in terms of bringing a 
design through a company to successful customer acceptance. Not just 
my opinion, it's history. 

This is what's wrong with grads, with respect to the electrcmics industry: 

They are not ready to make money for their new employer. 

They don't know they're not scientists; that engineers make and sell 
things. They don't appreciate the economic foundation we all oper- 
ate with. 

They don't know just how under-prepared they are. Hiey are Sopho- 
mores — from the ancient Greek, suggesting "those who think they 
know." They try to change that which they don't really understand. 
They have hubriSy the unearned egotistical satisfaction of the young 
and the matriculated. 

They see that many of their superiors are jerks, idiots, incompetents, 
or lazy. Well, sure. Not in all companies, but too often true enough. 
Our grads often proclaim this truth loudly and invite unnecessary 
trouble. 

They willingly accept tasks they are ill-suited for. They don't know 
they'll be slaughtered for their failures. Marketing positions come 
to mind. 

Not all grads actually like engineering. They might have taken the 
career for monetary reward alone. These folks may never be good 
at the trade. 

So, should we never hire young engineers? Should we declare them 
useless and damn them to eternal disgrace? Should we never party with 
them? Well, probably not. I can see that at Elantec, a relatively young and 
growing company, we need them now and will esp^ially nead them when 
we old farts get more lethargic. It's simple economics; as cdnq>toies grow 



10 



they need more people to get more work done. Anyway, young people 
really do add vitality to our aging industry. 

It behooves us all, then, to create a professional growth path where the 
company can get the most out of its investment, and the new grad can 
also get the most lifelong result from his or her college investment. I have 
a practical plan. I didn't invent it; the Renaissance tradespeople did. It's 
called "apprenticeship." 

The "crafts" were developed in the 1400s, mostly in Italy. The work 
was the production of household art. This might be devotional paintings, 
could be wondrous inlaid marble tables, might be gorgeous hand-woven 
tapestries to insulate the walls. In most cases, the artistic was combined 
with the practical. Let me amplify: the art was profitable. There was no 
cynicism about it; beauty and commerce were both considered good. 

We have simile attitudes today, but perhaps we've lost some of the 
artistic content. Too bad: our industrial management has very little imagi- 
nation, and seldom recognizes the value of beauty in the marketplace. At 
Elantec, we've made our reputation on being the analog boutique of 
high-speed circuits. We couldn't compete on pure price as a younger 
company, but our willingness to make elegant circuits gave us a lot of 
customer loyalty. We let the big companies offer cheap but ugly circuits; 
we try to give customers their ideal integrated solutions. We truly like our 
customers and want to please them. We are finally competitive in pricing, 
but we still offer a lot of value in the cheaper circuits. 

Do college grads figure into this market approach? Not at all. You 
can' t expect the grad to immediately understand the m^ffketplace, the 
management of reliable manufacturing, or even effective design right out 
of college. Just ain't taught. The Renaissance concept of the "shop" will 
work, however. The shop was a training place, a place where ability was 
measured rather than assumed, where each employee was assigned tasks 
aimed for success. Professional growth was managed. 

An example: the Renaissance portrait shop. The frame was con- 
structed by the lowliest of apprentices. This frame was carved wood, and 
the apprentice spent much of his or her time practicing carving on junk 
wood in anticipation of real product. The frame apprentice also was 
taught how to suspend the canvas properly. Much of the area of the can- 
vas was painted by other apprentices or journeyman painters. They were 
allowed to paint only cherubs or buildings or clouds. The young painters 
were encouraged to form such small specialties, for they support deeper 
abilities later. So many fine old paintings were done by gangs; it's sur- 
prising. Raphael, Tintoretto, and even Michelangelo had such shops. The 
masters, of course, directed the design and support effort, but made the 
dominant im^^es we attribute to them alone. Most of the master painters 
had been apprentices in someone else's shops. We get our phrase "state 
of the art" from these people. 

Today's engineers do practice an art form. Our management would 
probably prefer that we not recognize the art content, for it derails 



How to Grow Strong, Healthy Engineers 



traditional business management based on power. We engineers have to 
ensure that artistic and practical training be given to our novices. 

So, how does one train the engineering grad? I can only speak for my 
own field, analog IC design. I'll give some suggestions that will have 
equivalents in other areas of engineering. The reader can create a pro- 
gram for his or her own work. 

1. The grad will initially be given applications engineering duty. 
Applications is the company's technical link with the buying public. TOs 
group answers phone calls of technical inquiries and helps customers 
with specific problems with the circuits in the lab, when published or 
designer information is unavailable. Phone duty is only half of applica- 
tions; they develop applications circuits utilizing products and get the 
write-ups published, typically through trade magazines such as EDN. 
They produce application notes, which serve as practical and educational 
reading for customers. A well-developed department will also create <tota 
sheets, hfting the burden from the designers but also enforcing a level of 
quality and similarity in the company's literature. My first two years in 
the industry were in this job. In one instance, I forced a redesign of a 
circuit I was preparing the data sheet for because it simply did not func- 
tion adequately for the end application. Of course, designers always think 
their circuits are good enough. A truly seasoned applications engineer 
can be involve in new product selection. 

The point of this assignment is to teach future designers what to 
design, what customers need (as opposed to what they want), how to 
interact with the factory, and general market information* I wouldn't let 
new grads speak to customers immediately; first they would make data 
sheets for new products and be required to play with circuits in the lab to 
become familiar with the product line. Making application notes would 
be required, guided by senior applications engineers. I believe thM devel- 
oping good engineering writing skills is important for the designer. 

After a couple of months, the engineer would start phone duty. I 
think the first few calls should be handled with a senior apps engineer 
listening, to coach the young en^neer after the calls. It's important that 
the engineer be optimally professional and helpful to the customer so as 
to represent the company best. Most of us have called other companies 
for help with some product problem, only to reach some useless clone. 

This stint in applications would last full-time for six months, then be 
continued another six months half-time, say mornings for us West Coast 
folks. 

2* Device modeling would be the next part-time assignment. In ana- 
log IC circuit design, it's very important to use accurate and extensive 
model parameters for the circuit simulators. Not having good models has 
caused extensive redesign exercises in our early days, and most designers 
in the industry never have adequate models. As circuits get faster and 
faster, this becomes even more critical. Larger companies have modeling 

12 



groups, or require the process development engineers to create models. I 
have found these groups' data inaccurate in the previous companies where 
Fve worked. We recently checked for accuracy between some device 
samples and the models created by a modeling group at a well-known 
simulator vendor, and the data was pure garbage. We modeled the devices 
correctly ourselves. 

This being a general design need, I would have the young engineer 
create model parameters from process samples, guided by a senior engi- 
neer with a knack for the subject. This would also be an opportunity to 
steep the engineer in the simulation procedures of the department, since 
the models are verified and adjusted by using them in the circuit simulator 
to play back the initial measurements. It's a pretty tedious task, involving 
lots of careful measurements and extrapolations, and would probably take 
three months, part-time, to re-characterize a process. Modeling does give 
the engineer truly fundamental knowledge about device limitations in 
circuits and geometries appropriate to different circuit applications, some 
really arcane and useful laboratory techniques, and the appreciation for 
accuracy and detail needed in design. 

Because of the tedium of modeling, few companies have accurate 
ongoing process data. 

3, A couple of layouts would then be appropriate. Most of our de- 
signers at Elantec have done the mask design for some of their circuits, 
but this is rare in the industry. The usual approach is to give inadequate 
design packages to professional mask designers and waste much of their 
time badgering them through the layout. The designer often does an inad- 
equate check of the finished layout, occasionally insisting on changes in 
areas that should have been edited earlier. When the project runs late, the 
engineer can blame the mask designer. You see it all the time. 

I would have the young engineer take the job of mask designer for 
one easy layout in the second three months of half-time. He would lay 
out another designer's circuit and observe all the inefficiencies heaped 
upon him, hopefully with an eye to preventing them in the future. Actu- 
ally, we designers have found it very enlightening to draw our own cir- 
cuits here; you get a feel for what kind of circuitry packs well on a die 
and what is good packing, and you confront issues of component match- 
ing and current/power densities. The designer also gains the abihty to 
predict the die size of circuits before layout The ultimate gain is in im- 
proving engineers* ability to manage a project involving other people. 

4. The first real design can be started at the beginning of the second 
year. This should be a design with success guaranteed, such as splicing 
the existing circuit A with the existing circuit B; no creativity desired but 
economy required. Hiis is a trend in modem analog IC design: elaborating 
functions around proven working circuitry. The engineer will be overseen 
by a senior engineer, possibly the designer of the existing circuitry to be 
retrofitted. The senior engineer should be given management power over 



How to Grow Strong, Healthy Engineers 



the young engineer, and should be held responsible for the project results. 
We should not invest project leadership too early in young engineers; it's 
not fair to them. The engineer will also lay the circuit out, characterize it, 
and make the data sheet. Each step should be overseen by an appropriate 
senior engineer. This phase is a full-time effort for about five months for 
design, is in ^yance while waiting for silicon, and fuU^tin^ again for 
about two months during characterization. 

5, The first solo design can now begin. The engimer now has been 
led through each of the steps in a design, except for product development. 
Here the designer (we'll call the young engineer a designer only when the 
first product is delivered to production) takes the project details from the 
marketing department and reforms them to a more producible definition 
of siUcon. At the end of the initial product planning, the designer can 
report to the company what the expected specifications, functionality, and 
die size are. There are always difficulties and trade-offs that modify mar- 
keting's initial request. This should be overseen by the design manager. 
The project will presumably continue through the now-fanwliar sequence. 
The designer should be allowed to utilize a mask designer at this point, 
but should probably characterize the silicon and write the data sheet one 
last time. 

This regimen takes a little over two years, but is valuable to the com- 
pany right from the start. In the long mn, the company gains a seasoned 
designer in about three years, not the usual seven years minimum. It's 
also an opportunity to see where a prospective designer will have difficul- 
ties without incurring devastating emotional and project damage. The 
grad can decide for himself or herself if the design path is really correct, 
and the apprenticeship gives opportunities to jump into other career paths. 

I like the concepts of apprentice, journeyman, and master levels of the 
art. If you hang around in the industry long enough, you'll get the title 
"senior" or "staff." It's title inflation. I have met very few masters at our 
craft; most of us fall into the journeyman category. I put no union con- 
notation on the terms; I just like the emphasis on craftsmanship. 

There are a few engineers who graduate ready to make a company 
some money, but very few. Most grads are fresh engineering meat, and 
need to be developed into real engineers. It's time for companies to train 
their people and eliminate the undeserved failures. I worked for five years 
at a well-known IC company that was fond of bragging that it rolled 20% 
of its income into research and development. The fact is, it was so poorly 
organized that the majority of development projects failed ^^'le projects 
were poorly managed, and the company was fond of "throwuig a designer 
and a project against the wall and seeing which ones stick " Most of the 
designers thrown were recent graduates. 

We should guide grads through this kind of apprenticeship to preserve 
their enthusiasm and energy, ensuring a better profession for us all. 



14 



When I read the first Williams compendium (the precursor to this 
book), I was shocked by the travelogs and editorials and downright per- 
sonal writings. Myself, I specialize in purely technical writing. But after 
Jim gave me the opportunity to offer something for the second book, the 
first book seemed more right and I couldn't resist this chance for blatant 
editorialization. Fm mad, see, mad about the waste of young engineers. 
Waste is bad. 



This page intentionally left blank 



Barry Harvey 



3. We Used to Get Burned a Lot, 

and We Liked It 



I'm a fortunate engineer. My employer sponsors the hobby I've had for 
thirty of my forty-year life. We don't disagree much; I like most of the 
aspects of my job, even the tedious ones. However, I'm no lackey. I don't 
really listen to many people, although I try to appear to. There's no cyni- 
cism here; all my associates agree with me that we will produce nifty 
new ICs and make money. That's the job. 

This entry of Jim's compendium is offered to relate what an earlier 
generation of engineers experienced in preparation for a career in elec- 
tronics. Many of my associates were quite functional in electronics when 
they entered college. We were apparently different from most of the stu- 
dents today. We were self-directed and motivated, and liked the subject. I 
have detected a gradual decrease in proficiency and enthusiasm in college 
graduates over the last fifteen years; perhaps this writing will explain 
some of the attitudes of their seniors. I've included some photographs of 
lovely old tube equipment as background. 

My experiences with electronics started with constmction projects in- 
volving vacuum tubes, then transistors, eventually analog ICs, raw micro- 
processor boards, and finally the design of high-frequency analog ICs. 
Through all the years, I've tried to keep the hobby attitude alive. I'm not 
patient enough to grind through a job for years on end if I don't really enjoy 
it. I recommend that anyone who finds his or her job boring decide what 
they do like to do, quit the current job, and do the more enjoyable thing. 

My first memory of vacuum tubes is a hot Las Vegas, Nevada morning 
around 1 a.m. I was young, about ten years old. It was too hot to sleep 
and the AM radio was gushing out Johnny Cash, Beach Boys, Beatles, 
and the House of the Rising Sun, as well as cowboy music. It was pretty 
psychedelic stuff for the time, and with a temperature of lOO'^F at night, 
the low humidity and the rarefied air, I spent a lot of late nights awake 
with the radio. 

As I lay listening to the music I noticed that the tubes of the radio 
projected more blue light on the ceiling than the expected yellow-red 
filament glow. It's hard to imagine that simple, beautiful, blue projection 
upon your wall which comes from the miniature infemo within the tubes. 
It comes from argon gas which leaks into the tube and fluoresces in the 
electric fields within. Occasionally, you can see the music modulate the 
light of the output tubes. 



17 



We Used to Get Burned a Lot, and We Liked It 



My radio, which sat next to my bed so that I could run it quietly with- 
out waking the parents, was a humble GE table model. It was built in the 
mid-50s, so it was made of cheap pine with ash (or maple?) veneer. Typ- 
ical of the times, it had sweeping rounded comers between the top and 
front, and inlaid edging. They never did figure out how to make a true 
accurate comer with cheap wood processes. This radio was B-gmde, 
though; it had a magic-eye tube and included the '*MW" band-low MHz 
AM reception. Allegedly, you could hear ships and commercial service on 
MW, but in Las Vegas all I heard were ham radio 1 ,8MHz **rag chewer" 
conversations. At length. 

Radios were magic then, TV wasn't nearly as entrancing as now, being 
black-and white in most homes and generally inane (the good adult stuff 
was on too late for me to see). On radio you heard world news, pretty 
much the only up-to-the-minute news. You heard radio stations that didn't 
know from anything but variety in music. They didn*t go for demograph- 
ics or intense advertising; they just tried to be amusing. When I was that 
young, the people who called into the talk shows were trying to be intelli- 
gent, Shows what an old fart I am. 

The electronic product market of the time was mostly TV and radios. 
Interestingly, the quality living-room TV of that time cost around $600, 
just like now. Then you also got a big console, radio, speakers, and 




Figure 3-1 

A lovely TRF radio from the 1920s and '30s. This was before superheterodyne reception; you had to tune ail 
three dials to get your station. More or !ess gain was dialed in with the rheostats in series with the input tubes' 
filaments. A lot of fami as well as city dwellers used these. The coils were hand-wound, and every component 
was available for scrutiny This set will be usable after a nuclear attack. From the John Eckland Collection, Palo 
Alto, California. Photo by Caleb Brown. 



record player for the price (it even played a stack of records in sequence). 
It worked poorly, but it was a HOME ENTERTAINMENT SYSTEM. We 
pay only a little more for similar but better today. Lab equipment was 
really rotten then compared to today. There was no digital anything. 
Want to measure a voltage? You get a meter, and if you're lucky it has a 
vacuum-tube amplifier to improve its range, versatility, and resistance to 
burnout, I couldn't afford one; I had a 20Kf2/ V multimeter. I eventually 
did wreck it, using it on a wrong range. 

In the vacuum-tube days, things burned out. The tubes might only last 
a year, or they might last 20 years. Early 2- watt resistors had wax in 
them, and always burned out. The later carbon resistors could still bum 
out. When 1 say bum out, I mean exactly that: they went up in smoke 
or even flame. That's where the term came from. Where we have cute 
switching power supplies today, then the tubes ran from what we call 
"linear" supplies that included power transformers which in quality gear 
weighed a dozen pounds or more. The rectifiers might be massive tubes, 
or they could be selenium rectifiers that also burned up, and they were 
poisonous when they did. The bypass capacitors were a joke. They would 
eventually fail and spew out a caustic goop on the rest of the innocent 
electronics. Let's face it, this stuff was dangerous. 

I almost forgot to mention the heat. A typical vacuum tube ran hot; the 
glass would bum you if you touched it. The wood cabinets needed to be 
regularly oiled or waxed because the heat inside discolored and cooked 
them. A power tube ran really hot, hot enough to make the plate glow 
cherry-red in normal operation. You could get an infrared sunburn from 
a few inches' proximity to a serious power tube. From a couple of feet 
away your face would feel the heat from an operating transmitter. 

But it wasn't bumout or heat that was the most dangerous thing to an 
electronics enthusiast; it was the voltage. The very wimpiest tube ran 
from 45V plate potential, but the usual voltage was more like 200V for a 
low-power circuit. I made a beautiful supply for my ham transmitter that 
provided 750V for the output amplifier. Naturally, it knocked me across 
the room one day when I touched the wrong thing; a kind of coming-of- 
age ritual. This event relieved me of all fear of electricity, and it gave me 
m inclination to think before acting. Nowadays, I sneer at bare electrodes 
connected to semiconductors. I routinely touch nodes to monitor the ef- 
fect of body capacitance and damping on circuit behavior. I have often 
amazed gullible peasants by curing oscillations or fixing bypasses with 
only my touch. Of course, the off-line power supplies command my re- 
spect. For them, I submit and use an isolation transformer. 

At this point, I think we can explain the lack of females attracted to 
electronics at Ae time. In the 50s md 60s, society protected women but 
offered men up to danger. The same is tme for the earlier industrial revo- 
lution: women were huddled into protective work environments and men 
were fodder for the dangerous jobs. I think this attitude was prevalent 
with respect to vacuum tube electronics. Women (girls, in particular) 



We Used to Get Burned a Lot, and We Uked It 



were not encouraged to enjoy the shock hazards, the bums, the excessive 
weights of the equipment, or the dirtiness of the surfaces. 

Boys, of course, found all this attractive. I suppose this is the historical 
basis of the male domination of the field. The duress of dealing with this 
kind of electronics really appealed to young men's macho, just like work- 
ing on cars appealed to the gearhead set. The difference between the 
groups was that electronics required a lot more education and intellect 
than cars, and so appealed to more bookish types. The girls never caught 
on to how cool electronics was, probably because a radio can't get you out 
of the house. The electronics hobbyists (creators of today's nerd stereo- 
type) simply found another way to get away from the parents. It worked; 
the old folks really did keep out of the garage, the rightful dominion of 
hobby electronics. 

A social difference between then and now is how much more prevalent 
hobbies were. As I mentioned, TV did not occupy as much of people's 
time. Kids got as bored as now, so they turned to hobbies. When boys got 
together, they needed something to do, and they could share cars or elec- 
tronics, This led to a much more capable young workforce, and getting a 
job after high school seemed easier than now. Furthermore, you probably 
had strong interests that could guide you through college. Changing ma- 
jors or not having a major was unusual. Now, kids are generally far less 
self'directed. They haven't had to resolve boredom; there's too much en- 




Figure 3-2. 

An original breacfcoard. The components are on the board, and hopefully Ma has another This i$ a phonogrs^ 
pre-amp and power amplifier, just like 1930-to-1960 home project assemblies. You can really see your solder 
joints in this construction style. From the John Eckiand Collection, Palo Alto, California. Photo by Caleb Brown. 



Barry Harvey 



tertainment easily available to them today. Further, drugs destroy hobbies. 
As a result, the college students I've interviewed over the years have grad- 
ually lost pre-coUege experience with their field. Twenty years ago college 
grads had typically been working with electronics for two to seven years 
before college, and the new grad could perform well in industry. Regret- 
tably, it now takes up to three years of professional experience to build a 
junior engineer, titles notwithstanding. 

Perhaps worse is the attitude change over the years. The new grad was 
considered an amateur; ''amateur'* from the Latin, meaning ''one who 
loves a field": motivated but inexperienced. Iiicreasingly, the grads are in 
electronics for the bucks, and seldom play in the art for their own amuse- 
ment. Present company excepted; I know the readers of this book are not 
in that category. To be fair, present electronics focuses on computers and 
massive systems that are hard to comprehend or create in youth. Con- 
struction of projects or repairing home electronics is mostly out of the 
realm of kids not encouraged by a technical adult. 

I think this places an obligation on families and schools to support elec- 
tronics projects for kids, if we are to generate really capable and wise 
engineers in the future. By the time a present grad has had enough years 
of experience to become an expert in some area, the technology is liable 
to change. Breadth of technical experience is the only professional answer 




Rgure 3-3. 

A really beautiful radio from the 1 950s. A so-called Tombstone radio; the fins are wood decoration. This is elec- 
tronics as furniture; the radio is good but the cabinet is exquisite. The dial is artistic and several frequency bands 
await the curious. Not fully visible is the same radio flanked by different cabinets made by competitive groups 
within Zenith, From the John Eckland Collection, Palo Alto, California. Photo by Caleb Brown, 



We Used to Get Burned a Lot, and We Liked it 



to this problem. Employers do not encourage nor support the engineer's 
development outside his narrow field, so breadth seems something best 
developed by hobbies before college, and a more varied engineerinqg train- 
ing during college. 

But we digress. Somewhere around 1964 I saw the first transistor ra- 
dios. They were kind of a novelty; they didn't work too well and were 
notoriously unreliable. They replaced portable tube radios, which were 
just smaller than a child's lunch box. They weighed about seven pounds, 
and used a 45V or 67V battery and a couple of "D" cells for the fila- 
ments. The tubes were initially normal-sized but had low-power 
filaments in the portables, but the latest were socketless and had cases 
only IJ^" long and Vi diameter. These tubes were also used in satellites 
and were quite good. Even so, the transistor radios were instant winners. 
They were cheaper than any tube radio, were truly portstole, and could 
be hidden in classrooms. The miniature earphone really made it big. 

The transistor radio easily doubled the audience for musicians and 
advertisers. Perhaps it was the portable transistor radio that accounted for 
the explosive growth of rock music. . . . While it's true that rock-and-roll 
was popular as hell in the late 50s and early 60s, the sales of records and 
the number of radio stations just didn't compare with the activity at the 
end of the 60s. 

As I said, the transistor radios were unreliable. I made spending money 
repairing radios when I was in grade school. Attempting to repair them; 
my hit ratio was only 50%. These repairs were on bad hand-sol^tered 
joints, on broken circuit boards (they were made of so-called Bakelite — a 
mixture of sawdust and resin), and unreliable volume controls. Replace- 
ment parts were grudgingly sold by TV repair shops; they'd rather do the 
servicing, thank you. Hie garbage line of 2SK-prefix transistors was of- 
fered. These Japanese part numbers had nothing to do with the American 
types and surprisingly few cross-references were available. I had no 
equipment, but most of the failures were due to gross construction or 
device quality problems. 

Only a few years after the transistor radios emerged they became too 
cheap to repair. They made for a poor hobby anyway, so I turned to ham 
radio. This was the world-wide society of folks who lUce to taBc to each 
other. The farther away the better; it's more fun to talk to a fellow in 
Panama than one in Indiana. People were more sociable then, anyway. 
The world community seemed comfortably far off and "foreign" had an 
attraction. 

I didn't have enough money to buy real commercial ham gear. Luckily 
for me, many hams had the same inclinations as I and a dynamic home- 
construction craze was ongoing. Hams would build any part of a radio 
station: receivers, transmitters, or antennas. They were quite a game 
group (of mostly guys), actually; grounded in physics and algebra, they 
used little calibrated equipment but actually furthered the state of radio 
art. Congress gave them wide expanses of spectrum to support this re- 
naissance of American engineering. We got a generation of proficient 



22 



Barry Harvey 



Figur* 3-4. 

Here*s the chassis of a first-rate radio. The base metal is chrome-plated for longevity. All coils are shielded in 
plated housings, and string tuning indicator mechanisms are replaced with steel wire, These components are as 
uncorrupted as they were when they were made in 1960. The designers gave extra attention to the quality of 
everything the customer would see and feel (the knobs play very well). From the John Eckland Collection, Palo 
Alto, California, Photo by Caleb Brown. 




engineers from radio. Hams performed feats of moon bounce communi- 
cations and even made a series of Oscar repeater satellites. Imagine that, 
a group of civilians building satellites that NASA launched into space for 
free, I myself have heard aurora skip signals on the 6-meter band — ^the 
bouncing of signals off the northern lights* All this in the days of early 
space travel and Star Trek. Some fun. 

Soon after transistor radios were common, industrial transistors became 
cheap and available in volume. The hobby books were out with good cir- 
cuit ideas in them, so I finally started making transistor projects about 
1966. 1 was a bit reluctant at first, because the bipolars were delicate, 
physically and electrically, and had poor gain and frequency response. 
Tbbes were still superior for the hobbyist because of their availability. You 
could salvage parts from radios and TVs found at the dump, or discarded 
sets awaiting the trashman. Because the circuits were relatively simple, we 
would dismantle old sets right down to separated components and chassis, 
which would be reassembled into the next hobby project. I began to tap 
the surplus parts suppliers, and the added supply of tube and related parts 
delayed my interest in solid-state circuits. 

The first commercial transistors were germanium PNP, and they 
sucked. They just wouldn*t work correctly at high temperatures, and their 



We Used to Get Burned a Lot, and We Liked It 



Figure 3-5. 

A medium^uality table radio of the 1 950s. Being decorative, tlie cabinet and dial are of good quality, hi tlie 
upper-right corner is a magie-eye tube, an oscilioscope-lilte gizmo that gives an analog indication of tuning 
accuracy Rom the John Eckland Collection, Palo Alto, California. Photo by Caleb Brown. 




leakage currents skyrocketed past 100°C to the extent of debiasing cir- 
cuits. Their Vbe went to zero at IWC; that is, the whole transistor be- 
came intrinsic and was a short-circuit. Furthermore, you couldn*t find 
two devices that halfway matched with respect to Vbe and beta and out- 
put impedance. You didn't bother making instrumentation circuits with 
those devices; there just weren't any matched pairs to be found. The 
Vbe's also suffered from terrible long-term drift, I think because germa- 
nium could never be alloyed adequately for a solid contact. It didn't mat- 
ter; chopper-stabilized tube op amps were common and worked well I 
still have one of the best VTVMs ever made, a Hewlett-Packard chopper- 
stabilized model that has sensitive DC ranges and a 700MHz active AC 
probe. 

What really made my decision to use transistors was the advent of the 
silicon NPN device, Silicon could tolerate temperature, and was insensi- 
tive to excessive soldering- It never went intrinsic, and beta control al- 
lowed for matched pairs. The high-quality differential input stage made 
the industry of hybrid op amps possible, and some of them could handle 
the same signal voltages as the tube op amps. Silicon transistors even 
gave decent frequency responses, although the faster devices were still 
electrically delicate. Silicon made TVs and radios work better too. 

Circuit design changed overnight. The threshold voltage of tubes 
(analogous to the threshold of JFETs) would vary over a 3: 1 range. 
Because of the poor bias point accuracies, most circuits were AC cou- 
pled. This precluded them from many industrial applications. Although 



Bairy Harvey 



Figure 3-6. 

The electron^ of the previous radio. Because this set was not of the highest caliber^ the electronics are humble 
and have no precious elements. From the John Eckland Collection, Palo Alto, California. Photo by Caleb Brown. 




the chopper-stabilized op amp was very accurate, it was expensive and 
the chopper could wear out, being a mechanical vibrator. The uncertainty 
of transistor Vbe was really negligible, relative to supply voltages, and 
biasing transistors was a snap, although not widely understood then. 
Transistors could seemingly do anything that didn't involve too much 
power But until perhaps l%6, if you had to handle power with a transis- 
tor, you used a cow of a germanium device. 

But between 1961 and 1967, the choice of transistor or tube was often 
made by the prejudice of the designer. Some applications demanded one 
device or the other, but in the case of audio amplifiers, there was free 
choice. 

Construction of electronics changed radically in this time. Tubes were 
mounted in sockets whose lugs served as the supports for components, 
and a solid steel chassis supported the circuits. Steel was necessary, since 
the tubes couldn't tolerate mechanical vibration and the massive power 
supplies needed support. The most elegant construction was found in 
Tektronics oscilloscopes. They used molded ceramic terminal strips to 
support components, and only about eight components could be soldered 
into a pair of terminal strips. Cheaper products used Bakelite strips. 
These were all rather three-dimensional soldered assemblies: point-to* 
point wiring literally meant a carpet of components connected to each 
other and to mbes in space. The assemblies were also very three dimen- 
sional; the tubes sprouted vertically above the chassis by three to five 



We Used to Get Burned a Lot, and We Liked It 



inches and the other components sprawled in a two-inch mat below the 
chassis. 

Transistors made construction more two dimensional. Hie transistors 
weren't tall, generally the size of our TO-39 package of today, and circuit 
boards were practical since they didn't have to support heavy or hot com- 
ponents. All passive components became shc^ too. A layer of transistor 
circuitry thinned to one inch or less. There was a volume reduction of 
about 20:1 over equivalent tube circuits. For industrial electronics, how- 
ever, transistors afforded only a 2:1 overall product cost reduction. 

In the 1960s, the quality of csbim^ really degraded. Transistor equip- 
ment was considered cheap, relative to tube gear, and only received 
cheesy plastic cases. The paint and decals on the plastic rubbed or flaked 
off, and impact could shatter it altogether. Tube equipment, on the other 
hand, bad enjoyed quality wood casings for decades. Since the tube chas- 
sis were so large and heavy, furniture-quality cabinets were needed sim- 
ply to transport the electronics. The radios and TVs were so obtrusive in 
tube forni that manufacturers really made the cabinets fine furniture to 
comply with home decor. 

Quality in the tube years came to mean both mass and the use of pre- 
cious materials. Greater mass meant you could transport or physically 
abuse the equipment with no damage. It also meant that the components 
would suffer less from thermal changes and microphonics felcctrical sen- 
sitivity to mechanical vibrations). A really sturdy chassis would not need 
alignment of the tuned circuits as often as a flimsy frame. Pracious mate- 
rials included quality platings — such as chrome or vanadium — of the 
chassis, to avoid corrosion and extend useful Ufe. Heavier transformers 
allowed more power for better bass response and greater volume, A heav- 
ier power transformer would bum out less frequently, as would oversize 
power tubes. Components came in quality levels from cheap organic- 
based resistors and capacitors that cockroaches could eat to more expen- 
sive and long-lived sealed components. The general attitude about 
electronics construction was akin to furniture: the more mass and the 
more precious the material, the better 

Since the transistor circuits had no thermal nor microphonic problems, 
the poorest of cases were given to them. They weighed next to nothing, 
and a hard fall wouldn't cause too much damage. Since the products had 
no mass nor special materials in their construction, people thought of 
transistor products as low-quality. The manufacturers made sott this was 
true by using the poorest materials available. The circuit boards did in- 
deed tamish and warp, and the copper could crack and cause opens. The 
wires soldered to the boards seemed always stressed from assembly and 
often broke. Even the solder had corrosive rosin. 

Because the transistor circuits were small, the traditional soldering 
guns and irons were far too hot and large to use; we now had to buy new 
small irons. We even had to get more delicate probes for oscilioseopes 
and voltmeters. These problems were moot; you couldn't effectively 
repair transistor stuff then anyway. Even if you could troubleshoot a bad 



26 



Bdrry Harvey 



Figurt 3-7. 

Electronics for the masses: the 1960 Knight-Kit audio amplifier. For $70, you get a l<it of parts and a chassis 
which can become a stereo 50W audio power amplifier This was a good deal; since labor was expensive, build- 
ing the thing at home saved money and the experience was somewhat educational More than 100,000 were 
sold. From the John Eckland Collection, Palo Atto, California. Photo by Caleb Brown. 




board, you had only a 50-50 chance of not damaging it when yon tried to 
replace a component. You could not make a profit repairing transistor 
products. 

It got harder to make hobby circuits too. In the mid'60s, printed circuit 
boards were so bad you might as well try to make your own. So I bought 
a bottle of ferric chloride and tried it myself. For masking, I tried direct 
painting (house exterior paint wasn't bad) and resist ink pens. This sort 
of worked; I had to blob-solder across many splits in the copper of my 
homemade boards, "Hobby boards*' were the solution. These are the pre- 
etched general-purpose breadboards in printed circuit form. They had 
DIP package regions and general O.T* spacing solder holes. Analog hob- 
byists would obediently solder interconnect wires between pads, but the 
digital hobbyists had too many connections to make and adopted 
wire-wrap construction. 

Suddenly construction projects lost their artistic appeal. Tiibes arrayed 
on a chassis with custom wiring are very attractive* but the scrambled 
wire masses of transistor projects are about as pretty as a Brillo pad. You 
could hardly see the connections of transistor circuits, and this only got 
worse as ICs displaced groups of transistors, I knew a couple of old 
codgers who gave up hobby electronics due to failing eyesight. They 
wouldn*t have had trouble with tube projects. Funny thing was, semicon- 
ductor projects still cost as much as tube equivalents but were uglier, 
more difficult to build, and harder to debug and tune. 



We Used to Get Burned a Lot, and We Liked It 



Professional breadboards were similar to the hobbyboards until perhq)s 
the early '80s. At work you built circuits on higher-quality breadboards. 
But within only a few years, critical ICs were available in surface-mount 
packages, or more expensive and clumsy socketed alternatives. ITie pin 
count of the packages just skyrocketed. The sockets are expensive and 
fragile. A transition began which is almost complete today: breadboards 
are simply not attempted to develop each subsystem of a board; the first 
tentative schematic will be laid out on a full-fledged circuit board. Any 
corrections are simply implemented as board revisions. These boards 
contain mostly surface-mount components. This technique is not praeti* 
cal for the hobbyist, 

God, what a nightmare it is to troubleshoot these boards. They are 
generally multilayer and the individual traces can't be seen, so finding 
interconnects is impossible. The only connections that can be probed or 
modified are the IC's leads themselves. You generally can't read the 
markings on resistors or capacitors, because they are so small Develop- 
ment work is accomplished with stereo microscopes. 

So hobby electronics has taken a major beating in the last twenty 
years. It's become intellectually difficult to build a really significant proj- 
ect, to say nothing of increased expense and construction difficulty. This 
portends a generation of relatively green engineers who have only coltege 
experience with electronics. God help us. I suppose there still are some 
handy people, as demonstrated by the continuing component sales of 
Radio Shack. Too bad that they have diminished the component content 
of their stores over the years, and traditional hobby suppliers like Lafay- 
ette and Heathkit have altogether disappeared. There is no substitute for 
pre-college electronics experience. 

Gone too is the magic people used to see in electronics. As a kid, I saw 
that other kids and their parents were amazed that radios and TVs worked 
at all. Our folks used to think of installing a TV antenna as an electronics 
project. Parents gave their kids science toys. These were great; we had 
chemistry sets, metal construction kits, build-your-own-radio-from- 
household-junk sets, model rockets, crystal-growing kits, all sorts of 
great science projects. The television stations even kept Mr. Wizard alive, 
the weekly science experiment program. 

It seems now that people assume they can't understand science or 
technology, and accept this ignorance. Kind of like religious belief. Peo- 
ple S^m to enjoy technology less, and expect more. We even predict 
future advancements when we have no idea how to accomplish them. We 
don't give our young children these science toys, even though the kids 
would find them wondrous. Parents are imposing jaded attitudes on kids. 

This would be all right, except that electronics has grown in scope 
beyond the ability of college to teach it well. Students graduating today 
have insufficient breadth of knowledge of the field, and not enough depth 
to really take on a professional project. I don't blame them; it's probably 



28 



impossible to be the master of anything with a college diploma but no 

real experience. 

I don't know all of the answers, just the problem. As long as our soci- 
ety considers engineering unglamorous and nerdy, kids won't be attracted 
to it. Industry will wonder why young engineers are not highly produc- 
tive. Companies never really train people; they just give them opportuni- 
ties. We'll see a general malaise in design productivity, just as we now 
see a problem with software production. I could be getting carried away 
with all this, but we should promote science and technology as suitable 
hobbies for our kids. 



This page intentionally left blank 



Keitaro Sekine 

4. Analog Design Productivity and the 
Challenge of Creating Future 
Generations of Analog Engineers 



Introduction 



Recently, digital techniques are very commonly used in the fields of elec- 
tronics. According to the statistics taken by MITI (Figure 4-1), Japanese 
integrated circuits industry has shown a growth of 5.5 times in the last 
one decade (from 1980 to 1991). While digital ICs (MOS and bipolar 
digital) grew 6.24 times in this period, analog ICs did only 3.57 times. 
This reflects to a analog vs. digital percentage ratio, showing that analog 
decreases from 25.9% on 1980 to 16.7% on 1991 (Figure 4-2). From 
these facts, many people in the electronics fields might think that the age 
of analog has been finished. 





'80 


'85 


'90 


'91 


MOS Digital 


100 


346 


650 


691 


Bipolar Digital 


100 


352 


340 


336 


Total of Digital 


100 


348 


591 


624 


Linear 


100 


261 


309 


357 


Grand Total 


100 


325 


518 


555 



Figure 4-1. 

Percentage of 
Japanese IC 
production. 



Institute of Electronics, Information and Communication Engineers 
(lEICE), one of the largest academic societies in electronics fields in 
Japan, held special sessions to discuss many problems with respect to the 
analog technologies in Japan at the lEICE National Convention in 1989 
and again in 1992 chaired by the author. Both sessions attracted much 
more participants than expected and proved that many serious engineers 
were still recognizing the importance of analog technology. We discussed 
the present status of analog technologies, how to create new analog tech- 
nologies, how to hand them down to the next generation engineers and 
how to use CAD in design of analog circuits to enhance productivity. 
This paper is based on several discussions in these sessions and author 
would like to acknowledge to those who discussed on the problems. 



31 



Analog Design Productivity and the Challenge of Creating Future Generations of Analog Engineers 



Figure 4-2. 

Digital-Analog 
Percentage Ratio 
(MITI). 



MOS Digital 
Bipolar Digital 
Total of Digital 
Linear 
Grand Total 



'80 ^85 

60.0 63.9 

14.1 153 
74.1 79.2 
25,9 20.8 

100.0 100.0 



'90 ^91 

75.3 74.8 

9.2 8.5 

84.5 83.3 

15^ 16.7 

100.0 100.0 



To summarize those discussions, we could categorized the problems in 
to the following three major classes;^ 

First, because of many people cannot understand that analog circuits 
technologies are not out of date but they really a key to develop digital 
technologies, the number of students who want to learn analog circuits 
technologies are has been decreasing year by year. Even student who 
willingly study analog circuits tends to prefer computer simulation rather 
than experiments, so they lose a sensitivity to the real world. Accordingly 
this lead the results that only a very few number of universities in Japan 
still publish technical papers in the field of analog circuits. 

Secondly, in the industries, although the importance of the analog 
circuits technologies are aware, two things make the number of analog 
circuits engineer decreased: increasing production of digital hardware 
system need to increase digital circuits engineers, and analog engineers 
easily understand digital technologies. 

Third, while CAD makes design of digital system very popular, design 
of analog circuits are still difficult, it requires still expert's skill. It has 
very insufficient productivity. Besides it takes a long time to educate 
engineers to be an analog circuits expert. Finally many factories tend to 
change their main productions from analog to digital systems. 

Analog circuits, however, have many advantages over digital technolo- 
gies: very high functional densities for the same chip size, high speed 
abilities and high potentials. 

So we must make a effort to increase the number of analog engineer 
and to hand analog circuits technologies down to next generations. 



Analog Design Productivity 

CAD (Computer Aided Design, but some peoples think it as Computer 
Automated Design) has been widely adopted in the design of digital inte- 
grated circuits. Computers can do everything from logic synthesis to 
mask pattern generation, taking the place of average design engineers, 
only if they got functional specification of the system written in some 
high level descriptive language. Meanwhile analog circuits CAD also 
become in great request according to the rise of several novel technolo- 
gies such as personal communication system, multimedia and so on. 
because we have insufficient number of analog circuits design engineers 



32 



to cope with this situations. (The reason why they have been decreased 
shall be mentioned in later section of this paper.) But unfortunately it is 
believed that there should be no such a powerful analog CAD system like 
a digital for a while. 

Analog circuits design technologies have following features which 
prevent us from realizing unified approach schemes: 

h While digital systems can be described with a couple of logic 
equations in principle, specifications of mdlog circ;uits are too much 
complicated to describe in a clear format. For instance, it sometimes is 
requested to design **excellent sound quality HiFi amplifier." We have no 
definition for "excellent sound quality" at all. It depends on individual 
judgment, sotne feels good the others feels no good, Ustening to the 
same amplifier. Besides a feeling judgment, amplifier has many charac- 
teristic items such as gain, frequency characteristics, dynamic range, 
distortion, temperature characteristics, input and output impedance, 
power consumption and so on. And normally we could not find evident 
correspondence between these characteristic items and the total perfor- 
mance. 

2. Several specifications on a single circuit usually conflict each 
other, so many trade off should be indispensable during the design proce- 
dure, taking restrictions such as perfornKuice of devices available, cost, 
deadline etc. into account. As these compromises could be done with the 
designer's personal experience and knowledge, there was no straightfor- 
ward scheme to do them. There were many papers with respect to the 
optimization of electronic circuits, but difficulties are not in how to do it 
but in where one should place the goal. 

3. To design a good analog circuits, a step by step method is quite 
insufficient and a breakthrough should be mandatory. Only man of talents 
can do that. But perhaps he cannot explain how he comes to the break- 
through. 

4 There are many circuit topologies and their combinations to real- 
ize the same specification. It should be so difficult for CAD to get a 
unique solution. 

Above mentioned features of analog circuits design are based on very 
essential characteristics of analog. We can not write any program without 
the knowledge about how it works. We think "computer-automated- 
design" of analog circuits are still one of challenging problems for us. 

We have, however, powerftil tools for analog circuit design, a circuit 
sinmilator. Among them "SPICE" and its derivatives are widely used 
by the design engineers. It is very useful as far as he use as literally 
"computer-aided-design" tools. Circuit simulator requires good under- 
standing of circuits from the design engineer. We discussed about mer- 
its/demerits of using circuit simulator in the National Convention of 
lEICE in 1992 to find the following problems: 



Analog Design Productivity and the Challenge of Creating Future Generations of Analog EnginiNNS 

1. Simulator could be very useful only for design engineers who 
really understand how the circuit works. 

2. It is very difficult to simulate such a circuit as having more than 
two widely spread time constants, for instance PLL, AM/FM de~ 
tector, crystal oscillator 

3. It is also difficult to derive device parameters, and installed mo^l 
does not reflect many parasitic elements such as substrate current, 
parasitic transistors, thermal coupling etc. Some of them can be 
avoided by adding some appropriate circuits, however this is not 
so easy for the average engineers, 

4. It cannot cope with a variation of circuit topology. We need to 
rewrite net lists and restart program whenever we change a circuit 
topology. 

These show that circuit simulators are indeed user dependent program 
therefore it is very important to teach beginners how to use it. 

Although the author mentioned about the shadow of circuit simulator, 
it is still very powerful tool. Dr. Minoru Nagata, Director of Central 
Research Laboratory Hitachi Ltd., showed the following evidence as an 
example. 

In the past 2 years, analog LSI has been developing, number of tran- 
sistors per chip increases twice while available time for design de- 
creases two thirds. But design engineers have 20% decreased in their 
fail rate at the first cut. Dr. Nagata also said that layout productivity in- 
creased 10 times and design correction decreased one tenth during this 
period. He stressed that these result could not be got without circuit 
simulators. 

The author pointed out how Japanese engineers thinking about analog 
circuit design productivity and circuit simulator. However analog circuit 
design still strongly depends on the designer of talent. Comparing the 
design of logic system to analog circuit, we would find that an one of 
apparent difference between them is that analog circuits has usually more 
than one complex function while one logic circuit element has only one 
function. Most digital system designers think their design in logic ele- 
ment or logic gate level, while analog designs are carried out in circuit 
element level such as transistors, resistor etc. A resistor in collector circuit 
works as a voltage dropper and same time it governs gain and frequency 
characteristics of that circuit. Analog circuits design engineer should al- 
ways pay his attention to trade-off between these complex functions. 
Professional analog circuit designer is a man who knows these trade-off 
technology and who success to realize compact and high performance 
circuits. 

As demands for analog circuit rising, we should solve this design pro- 
ductivity problem. How could we make beginner or computer designed 
analog circuits? Professor Nobuo Fujii at Tokyo Institute of Technologies 
and other members in the Technical Committee for Analog Circuit Design 



34 



at Institute of Electrical Engineers of Japan (lEEJ), chaired by the author, 
has been discussed about these problem. We thought at first use of "Expert 
System'* which installed many loiowledge of experienced professi 
designers as a element functional circuit. We tried to categorize analog 
circuits by their function. However this idea did not work. Because of 
above mentioned reason, each circuit has complex functions, it was very 
cfifflcult to find functional element circuit in a database format. 

Analog systems can be described with a couple of differential equa- 
tions and "analog computer" is a tool to solve dilferential equation. 
Analog computer consist of some operational element such as integrator, 
adder, multiplier, limiter etc. Recently we come to the conclusion that by 
taking this operational circuit as an element we could compose any ana- 
log circuit using them in principle, although the circuit compactness 
sboold be lost. Several case studies in the committee show that this idea 
worfc^. There needs further investigation before this idea would be real. 

Armlog Cireuif Engmeers in Japanese Industry 

It is thought that rising digital technologies has been taking over analog 
circuits technologies. A number of laboratories in Japanese universities 
whose activities are in analog circuits fields, has been decreased recently. 
Dr. Minoru Nagata at Hitachi Ltd. questionnaired managers in several 
electronics factories to investigate what leading electronics engineers 
thinkir^ about^. 

The foUowings are the results of Dr. Nagata's questionnaires. 

QUESTIONNAIRE 1 

Q. How do you think about an ability of newcome electronics engi- 
neers at your company? Please choice from the fonowings. 

a) Newcomers know neither digital circuits nor analog circuit. 
Nothing about circuits technology. 

b) Newcomers know about digital circuit very well but nothing 
about analog circuits. 

c) Newcomers have average knowledge about either analog or digi- 
tal circuits. 

d) Newcomers know about analog circuit very well but nothing 
about digital circuits . 

e) Newcomers know about computer software very well but nothing 
about hardware technologies. 

RESULTS: 

a).... 24 b) .... 16 
c).... 11 d) .... 0 
e).... 26 



Analog Design Productivity and the Challenge of Creating Future Generations of Analog Engineers 
QUESTIONNAIRE 2 

Q. We have two professional circuit engineers, one is in digital and 
the other in analog, avail^te to add to your project troop. Which 
do you prefer, analog or digital? 

RESULTS: 

Analog 32(62%) Digital 20(38%) 
QUESTIONNAIRES 

Q. To support your urgent project, you can add ten more dreuit 
engineers to your troop. What ratio of engineers, analog to d%ital, 
do you like? 

RESULTS: 

10 digital engineers .,...1 

1 analog, 9 digital 1 

2 analog, 8 digital 14 

3 analog, 7 digital 16 

4 analog, 6 digital 9 

5 analog, 5 digital 2 

6 analog, 4 digital 3 

7 analog, 3 digital 3 

8 analog, 2 digital 2 

9 analog, 1 digital 0 

10 analog engineers 1 

Results of Questionnaire 1 confirm ttiat a few universities are inter- 
ested in analog circuit technology and most student are f ond of cdmfHiter 
software rather than hardware technology. This shows at the same time 
that most general people's interests are in digital field. It is, however, 
very interesting that industries need a lot of analog circuit engineers. Dr. 
Nagata said "Analog technology is a Key technology, while digital is a 
Main technology." It means that what governs the final performance of 
digital system such as speed and reliability is an analog circuit technol- 
ogy. Digital circuits are analog circuits in topological sense^ they use 
only two states of the circuits. Therefore faster the digital LSI, more trou- 
bles arise which analog technologies are mandatory to solve. 

As mentioned at the beginnings main productions of Jap^ese lC in- 
dustries are digital LSI, they need much digital circuit engineer to hold 
their production. It is difficult for a digital circuit engineer to understand 
rather complicated analog circuit, but to the contrary analog circuit engi- 
neer can easily design digital circuits. By this reason analog engineers 
are tend to be thrown into digital project, it forms one way flow (diode) 
of engineers from analog to digital, making the number of analog 
circuit engineers in the industry decreased year by year. Nevertheless 
many leading project managers become aware of importance of analog 
technologies. Results of questionnaire 2 and 3 seem to show this 
situation. 



36 



Recent high speed digital LSI such as memory and GPU requests 
much more analog circuit technology and digital signal processing sys- 
tem (DSP) need AD/DA converter at their interface most of which are 
aiialog circuits. Furthermore raising new system such as VHF/UHF com- 
munication, HDTV, multimedia etc. should request much analog circuit 
engineers. 

From historical view, in the field of high speed and high frequency, 
systems are implemented with analog technology at first, then according 
process technologies developing, they are took over by digital For exam- 
ple in communication digital system are implemented in 9.6 kbit/s, while 
eoax^ 400 Mbit/s and light 1.6 use analog technology. Another 
very interesting difference between two technologies are the number of 
transistors to realize the same function. Digital systems use a lot of tran- 
sistors while analog use only one himdreds or less transistors. (Unfortu- 
nately this does not mean that design of analog system needs less human 
resources including designer's skill.) 

To summarize, our industries become aware of importance of analog 
technologies and look for newcome analog engineer from university, but 
insufficient number of analog circuit engineers are supplied by universities. 

Creation and Education of Next-Generation Engineers 
at tlie University 

It is said recently that the number of Japanese high school students who 
want to take entrance examination for science or technology course of 
university has been decreasing year by year. Meanwhile the number of 
graduating students in technology course of university who want to get 
job at non-industrial company such as securities company and bank. For 
30 years ago most student in department of electronics selected their 
course because they wanted to be an electronics engineer. But at present 
time, more than two thirds of them Came with other reasons. In other 
words, many students in electronics course do not have their interest in 
electronics and study their curriculum only with a sense of duty. Instead, 
many students are fond of hitting a keyboard. They tend to play not in 
real world but in computer created virtual world. As a result, they think 
what circuit simulator outputs as a real circuit itself. Even young 
researcher in the doctor course sometimes write a paper using simulator 
only without simple experiment. 

This seems an origin of why young analog circuits engineers disap- 
pear. Our discussion at the National Convention came to the conclusion 
that it is because of disappearance of "Radio boy." Radio boy means such 
a boy who likes assembling parts to make a radio receiver, HiFi repro- 
ducer or transmitter as his hobby. We think many of them grew up to be 
analog engineers and play an important role in the development of Japan- 
&3it electronics industries. Professor Yanagisawa at Tokyo Institute 



Analog Design Productivity and tlie Cliallenge of Creating Future Generations of Analog Engineers 

Technology (now moves to Shibaura Institute Technology) pointed out 
that the criminal of disappearance of radio boy is spread of LSI into elec- 
tronics. LSI is quite a "black box'* and to look into a package of LSI cm 
never stimulate his curiosity! Therefore, in most university, professors are 
gradually increasing a percentage of basic experiments in their curricu- 
lum such as assembling a simple transistor circuits using a solder iron 
after designing it himself with a SPICE simulator. The author's experi- 
ence shows that most student are attracted by these type of experiments. 

The author believes that to increase "radio boy" is one of the most 
efficient means to increase good analog circuit engineers and it is an ur* 
gent matter for creating next generation analog engineer. Therefore i( is 
very important to create system which inspire young people to be inter- 
esting in real electronics world. We must pay our effort to looking for 
such a system. 

Conclusion 

The author describes several problems with respect to the analog circuits 
technologies in Japan, design productivities, challenge to creation and 
how hand them down to the next generations. Potential analog circuits 
engineer are decreasing here. But it should be stressed that analog circuit 
technologies are always necessary in the wave front region of electronics 
technologies, therefore the key technologies to develop much higher 
performance digital system and much high frequency circuits. So we 
must make as many younger peoples as possible to be interesting in 
learning analog technologies. 

Acknowlecigment 

The author acknowledges Dr. Minora Nagata at the Central Research 
Laboratory of Hitachi Ltd. for his encouragement and valuable advice. 
Thanks are also due to Professor Ken Yanagisawa, Professor Nobuo Fujii 
and Dr. Nagata for the permission to cite their opinions and discussions. 

References 

1. K. Sekine, "Creation and Hand down of Analog Circuit Technology Part 1 " Journal of 
IEICE13 (Sep. 1990): 1009-1010. 

2. K. Yanagisawa, "Creation and Hand down of Analog Circuit Technology Part 2," 
Journal of lElCE 13 (Sep. 1990): 1010-1011. 

3. M. Nagata, * 'Creation and Hand down of Analog Circuit Technology Part 3 " Journal 
oflEICE 73 (Sep. 1990): 1012-1015. 



38 



4. H. Yamada, ^'Creation and Hand down of Analog Circuit Technology Part 4," Journal 
cfIEICE13 (Sep. 1990): 1015-1017. 

5. N. Fujii» "Why Must You Study Analog Circuits in These Digital Technology Days?" 

Journal of lEICElK Aug, 1989): 925-928. 

6. K. Sekine, "Analysis and Design of Analog Circuits " lEEJ Papers of Technical 
Meeting on Electronic Circuits ECT92-14 (March 1992): 57-62. 



This page intentionally left blank 



Gregory T. A. Kovacs 



5. Thoughts on Becoming and Being an 

Analog Circuit Designer 

Special commentary by Laurel Beth Joyce, Greg's wife 

"My favorite programming language is solder." 

—Todd K. Whitehurst 
Stanford University, 1988 

Well, here I am, finally writing this book chapter! Instead of trying to 
tell the reader how to design analog circuits (I'll leave it to the folks with 
circuits named after them to do that, unless you take my courses), I will 
discuss several aspects of becoming and being an analog circuit designer. 
I will try to cover a few areas that I think are important, particularly to 
someone considering a career in this field. My wife's comments near the 
end of this chapter will also be of considerable interest to the significant 
other (S.O.) of anyone considering this career choice. 

Analog Circuit Designers 

What type of person becomes an analog circuit designer? Perhaps the 
best way to address that question is to start by describing the types of 
people who do not become analog circuit designers! Examples are folks 
whose second career choice would have been accounting, people who 
say "dude" a lot, people who have time to sit around wondering why 
their belly-button lint is gray,^ people who wear Birkenstock sandals and 
eat alfalfa, people who are frustrated by devices more complex than a 
paper clip, and people who are repeatedly abducted by space aliens. 

In other words, analog circuit designers tend to be a creative, practical, 
and curious bunch of folks who are rarely abducted by space aliens. The 
typical analog designer doesn't worry too much about shaving on week- 
ends (especially the female ones), drinks beer and eats pizza, owns an 
oscilloscope (see "Things You Need to Survive as a 'Real' Analog De- 
signer" below), thinks modem art consisting of blank white canvases is a 
bunch of crap, occasionally uses "swear words," and may be considered a 
bit "eccentric" by his or her friends and colleagues. Over the years, 
knowing a fair number of analog designers, I have only encountered one 
notable exception: Jim Williams.^ 



1 . Actually, my friends at the Office of Navel Research in Washington, DC, have studied this issue 
extensively. They have found that belly-button lint color is a complex function of clothing color, 
belly-button humidity, and the amount of cheese consumed. 

2. He doesn't drink beer. 

41 



Thoughts on Becoming and Being an Anaiog Circuit Designer 

Why should anyone want to become an analog designer? Aside from 
the large amounts of money you eam, the hordes of attractive members 
of the opposite sex that are drawn to you by the heady smell of solder, 
the ability to simulate circuits in your head, and the undying respect of 
all other engineers, there is one really important advantage to this line of 
work: it's fun! 

In fact, designing circuits can be absolutely wonderful. You create, 
from scratch, a complete working^ circuit that accomplishes a function 
you (or your boss) desire. Once you get some experience, you can visual- 
ize how the circuit building blocks you know can be combined; to get 
what you want. Sometimes you realize that you need to invent something 
really new to do a particular function. Creativity and a bit of insanity 
really helps with that. 

You don't need big power tools, a yard full of old cars up on blocks, or a 
trip to the Himalayas to build analog circuits. Actually, what you do need 
are small power tools, a garage full of old oscilloscopes up on blocks, and 
a trip to some surplus stores in Mountain View. In any case, once y ou reach 
some level of "analog enlightenment," it is really addictive. This is good, 
because the majority of engineers have gotten so seduced by digital circuits 
and software that some very big electronics companies exist that do not 
have a single decent analog circuit designer in house. In other words, if you 
learn analog circuit design, you can get a job! 

'I've heard enough! Sign me up!" If that's what you are thinking,'* you 
may want to know how you can become an analog designer. One way is 
to learn ''on the street" ("Hey buddy, wanna pick up some transistors 
cheap? . . . They've got high betas and they're clean!"). That works even- 
tually (the word "eventually" is key), but most people go to a university 
and learn there. If you are remotely interested in the latter option^ please 
read on . . . 



Analog Boot Camp: One Way to Become an 
Anaiog Designer 

I teach analog circuit design at Stanford,^ along with my colleagues in 
the Department of Electrical Engineering. In recent years, we have 
taken great pains to upgrade the electronics courses to include more 
practical, design-oriented material. My own courses are considered 
"analog boot camp" for undergraduates who think of transistors only in 



3. (eventually) 

4. (if not, please put this book down and read that biography of Bill Gates over there to the left) 

5. The opinions and/or other crap in this chapter are completely the fault of the author and do not 
reflect the opinions and/or other crap of Stanford University in any way. 



Gregory T. A. Kovacs 

terms of band diagrams. I'll share with you some of our "indoctrina- 
tion" techniques . . 

First, we adnrfnister an exam to weed out the people who should really 
be learning about French history or something like that. Here are a few 

sample questions: 

Choose the single best answer. 

1) The best all-around programming language is: 

a) C 

b) C++ 

c) BASIC 

d) Fortran 

e) solder 

2) A"GUrMs: 

a) a productivity-enhancing graphical user interface for modem com- 
puters 

b) useful for opening beer bottles 

c) a voltage regulation circuit invented by famous Dutch EE 
Cornelius von Fritzenfratz 

d) who gives a crap, this test is about analog circuits! 

3) Analog circuits are: 

a) circuits involving only resistors and capacitors, like in first-year 
electronics, dude 

b) circuits built with digital logic and no more than two discrete tran- 
sistors that you debug by reprogranuning EPROMS until they 
work 

c) not needed now that we have the "Newton" 

d) really cool 

4) SPICE is: 

a) stuff like salt and pepper you put on your food 

b) the reason nobody needs to build real circuits at all 

c) a program designed to see how quickly your computer bogs down 
when doing floating-point operations 

d) the only reason we need computers, other than Tetris.™ 

5) "Solder suckers" are: 

a) PG-rated, but can occasionally be seen on National Geographic 
specials 

b) the black holes of circuits, ofteii seen running around with current 
sources invented by Mr. Wilson (from **Dennis the Menace") 

c) people who are lured into analog circuit design by evil professors 

d) plastic pumps used to remove solder from component le^^ 
those uneducated about analog design have made mistakes 



6. These techniques have been developed over several decades by carefully selected teams of 
scientists from all over the world. 



43 



Thoughts on Becoming and Being an Analog Circuit Designer 

That sort of thing helps weed out the sick, the feeble-minded, and the 
history majors. Then we begin analog *'basic training " which involves 
learning the following song for drill practice and considerable healthful 
marching and shouting. 

Analog Boot Camp Drill Routine 

by G, Kovacs 

(The words are first barked out by the professor, then shouted back by 

students marching in formation.) 
Analog circuits sure are fine, 
Just can't get 'em off my mind. 

Digital circuits ain't my kind, 
Zeros and ones for simple minds. 

I guess NAND gates aren't all that bad, 
'Cause I need them for circuit CAD. 

One, two, three, four. 

Gain and bandwidth, we want more. 

Five, six, seven, eight, 
We don't want to oscillate. 

Widlar, Wilson, Brokaw too. 
They've got circuits, how 'bout you? 

{repeat) 

I also ask a few random questions and have been known to order a few 
push-ups here and there if, for example, a student cannot correctly distin- 
guish between the Miller and Budweiser Effects, Now the students are 
ready for their plunge into the world of analog . . . 

At this point, they are taught theory in one class and hands-on aspects 
in another. Essentially, the idea is to progress from the basic idea of an 
operational amplifier (op amp) through the necessary circuit building 
blocks that are required to design one. Finally, we reach the point where 
the students know enough to do that, and then we get into feedback and 
stability. Meanwhile, in the laboratory part of the class, the students are 
learning how to destroy most of the circuits covered in lecture. It is iti the 
lab that we teach them the all-important "smoke principle'* of solid-state 
devices. This is the formerly very closely guarded industrial secret that 
each discrete or integrated circuit is manufactured with a certain amount 



44 



Gregory t A. Kovaos 



of smoke pre-packaged inside. If, through an inadvertent wiring error, 
conditions arise through which the smoke is permitted to escape, the de- 
vice ceases to function. We also tmin the students to recognize and distin- 
guish the smells of different burning components ("Ah yes, a carbon 
resistor seems to have burned up in this circuit . . . smells like 220Kfl,"). 

I am not kidding about this, but not more than V^ of the EE students at 
this level have ever used a soldering iron before! In contrast, nearly all of 
them have driven a BMW and can explain leveraged buyouts in great 
detail (J presume this is a phenomenon more common at schools where 
yuppy pupae are present in large numbers). After a little trial and error, 
most of them leam which end of the soldering iron is hot (I am told that 
those who never really figure this out generally transfer to a local state- 
run university where they can just write software, but I have no concrete 
evidence of this). Pretty soon, they not only know how to solder, but also 
bow to use a wide range of up-to-date test equipment. (I worry about the 
ones who keep looking for an "auto setup" button on a voltmeter, though! 
. . . more on this below.) 

At this point, we get the students into the guts of Boot Camp: design 
it, SPICE it, make it work, and examine the differences between the 
SPICE model and the real thing. The idea is to teach simulation as "vir- 
tual instruments" and then introduce the real ones (the type with knobs). 
We provide SPICE decks^ for each circuit that are already on the student 
computers. We leave out critical component values for the students to 
choose. They have to come to lab with a running simulation and then 
bdild the circuit. This can be fun to watch the first time, as the students 
]r>ok around the lab for 10,000 amp current sources, diodes with forward 
voltages of exactly 0.700 V, and 13.4567E3 ohm resistors. Eventually, 
they figure things out and get things working.^ 

We ask them to sinmlate and build a lot of discrete circuits, including 
power supplies, basic op amp circuits, single-transistor amplifiers, a sim- 
ple op amp built from discretes, and power amplifiers. After that they 
build a project of their own choosing, demonstrating their analog design 
skills. This exercise gives them a chance to construct a complete circuit 
from scratch and write an instruction manual, specification sheet, and 
marketing sheet for whatever it is. Some students have built really amaz- 
ing things, such as a waveform synthesizer, a heterodyne spectrum ana- 
lyzer, an infrared remote control system, an acoustic rangefinder, etc. 
Some have built devices that are also humorous, including a fake leopard 



7, "lOBe^ Dad. why do they call them SPICE decks?" 

*1IWI, idil, Wiy back before they found a practical use for the *Newton* in 2027, computers used 
punched paper cards as a way to enter data and programs. We called a stack of those cards a 

'deck';' 

8. Our current sources only go to 9,000 amps, we keep the 0.700-V diodes in another room, and 
they need to specify resistor values to a few more decimals or our component supplier doesn't 
know which value to provide. 



45 



Thoughts on Becoming and Being an Anaiog Circuit Designer 

far-covered^ laser/galvanometer system for a light show, a guitar ampli- 
fier that **goes to eleven," and a contraption that the student pfoudly de- 
scribed as a "large vibrator" (he meant "multivibrator," but it was terribly 
funny at the time). 

Does it work? Are we able to turn out decent analog designers? Well, it 
seems to be working, and feedback from companies who have hired our 
students is positive. For me, success can be measured by the number of 
students who actually learn to love analog circuit design despite the fact 
that they are growing up in a world devoid of Heathkits and basements 
full of surplus electronics to hack circuits with. 

To illustrate the transformations that occur, I have reproduced a letter 
home from one of the students on his first and last days in Boot Camp 
(the names have been changed to protect the student's identity): 

Day 1 of Boot Canfip: 

Dear Mom, 

Things are going fine here at Stanford! Today we leanied 
about "operational ampUfiers They are triangle-shaped things that 
can do basically anything. The textbook says they have an "ideal 
voltage source" inside. Tell Pop that this means I can hook one up to 
power the whole farm when I get home this summer! I can't wait! 

Love, 

Billy 

Last day of Boot Camp: 

Dear Mom, 

I just finished my analog circuit training at Stanford! I now 
know I was wrong about operational amplifiers being able to power 
the whole farm! That was totally silly, because they are simpiy inte- 
grated circuits, and thus require external power. Also, their non-zero 
output resistance and short-circuit protection circuitry means that 
they can only supply a few milliamps of current. 

Do you know why smoke comes out of transistors when they 
get too hot? I will explain it all to you. Pop, and the farmhands 
when I get back there in a few weeks. 

I think we should consider turning the bam into a circuit de- 
sign laboratory. Bossie could stay in my room, since I will probably 
spend most of my time out there. Please let me know if this is OK, 
because I would rather do this than take a job doing software- 



9. Of course, we use only fake leopard fur because it is an endangered species, and we are ver>' 

politically correct. The only type of skin that is still OK to use for decorative purposes is that of 

Caucasian heterosexual males, but we were out of it at the time, 
10. We all know that positive feedback can lead to oscillations, so we will have to keep an eye on 

this situation. Raising tuition seems to provide the necessary negative feedback to keep the 

system stable. 



46 



Gregory T. A. Kovacs 



simulated power consumption validation of a subset of indirect-jump 
instructions of the new Valium computer chip at Interola's new lab 
in Lumbago, Oregon. 

Love, 

Billy 

What Should Aspiring Analog Designers Read? 

There is good stuff on analog circuits to read out there, aiid generally it is 
reasonably easy to locate. I am not going to go into the large number of 
books available other than to point out that you really need to have 
Horowitz and Hill, The Art of Electronics (Cambridge Press) and Gray 
and Meyer, Analysis and Design of Analog Integrated Circuits (John 
Wiley and Sons). Those two books are simply the essentials;^^ it's easy to 
supplement them from the droves of texts out there. 

As far as journals go, there are several good ones out there. Of course, 
the IEEE has a few. Then there's Wireless World, put out by a bunch of 
hackers in the United Kingdom, with real depth mixed right in there with 
fiiHi projeicts. Aiiother good foreign offering is Elektor, which is put out 
by a bunch of hackers in Holland (the closed-loop cheese fondue con- 
troller project last year was awesome). The Computer Applications 
Jourrml is^lim Circuit Sewer) is worth reading, but is aimed at those who 
thmk debugging a piece of hardware involves mainly fixing software (it 
is 90% digital subject matter, with occasional forays into scary things 
like op amps). What about those old standards like Popular Electronics? 
Well, they are OK for the occasional project idea, but as for technical 
content, I generally say, "Later!" (especially to ones with names like 
Electronics Now!). 

One of the richest sources of information, and probably the least obvi- 
ous to beginners, is the application notes written by the manufacturers of 
integrated circuits. Just think about it . . . they are trying to sell their 
wares by getting you excited about their uses.^^ They are absolutely 
packed with interesting cbcuits? Usually, you can get them for free, as 
well ^ sets of data books, just by calling the manufacturers. Saying you 
are a student usually helps, and will often get you free samples too. In 
case you don't know, the best ones are from National Semiconductor, 
Linear Technology, Maxim, Analog Devices, and Burr Brown. 



1 1 . Did I mention that this book is also one of the essentials? In any case, you are already clever 
enough to be reading it, so why bother! 

12. They have to accomplish this by showing you cool cirquits you can build, as op|}Qsed to tradi- 
tional marketing approaches, such as those used to sell beer. I am still waiting for the Swedish 
Bipolar Bikini Team, though! 



47 



Thoughts on Becoming and Being an Analog Circuit Designer 



Things You Need to Survive as a "Real" Analog 
Designer 

I am occasionally asked what you need to survive as a "real" analog de- 
signer. Well, this is a highly personal matter, but I can at least give my 
standard answer, which is the things I need (in order of importance): 

1 . An understanding significant other (S.O.) 

2. A laboratory dog to keep my feet warm 

3. A basic supply of discrete and integrated components 

4. A decent oscilloscope 

5. A power supply 

6. A soldering iron 

7. Basic hand tools 

8. Cheap beer 

9. A pad and pencil 

An understanding S,0. is critical, because when you start coming 
home with large chunks of blue-colored equipment and go misty-eyed 
when you see an old Tektronix catalog, it takes a special kind of person 
to understand! Analog designers tend to build up huge collections of old 
oscilloscopes, circuit boards, random metal boxes, and all sorts of *'pre- 
cious*' items that will come in handy some day. I think meeting an analog 
designer who isn't a packrat is about as likely as meeting the Swedish 
Bipolar Bikini Team, 

A typical workbench for analog circuit design is shown in Figure 5-1 * 
In addition, the "analog workstation,*' where most of the really good cir- 
cuit ideas are developed, is shown in Figure 5-2. The very useful labora- 



Gregory T A. Kovacs 




Figure 5-2. 

An analog work 
station. This is the 
place many great 
circuit designs are 
developed. 



tory dog (black Labrador called Rosie) is shown in Figure 5-3, She is 
better with a soldering iron than most engineers I know! 

Comments on Test Instruments 

Good test instruments are critical to a person's success as an analog cir- 
cuit designer! They are the equivalents of musical instruments to a musi- 
cian , . . you never share your Stradivarius (i.e.* Tektronix 7904A 
oscilloscope) and need to be intimately familiar with its nuances to get 
the best performance out of it. Bottom lines here: 1 ) don't buy cheesy 
foreign test gear unless you absolutely have to, and 2) when you find 




Rosie. the labora- 
tory dog in our 
house. She will 
debug any 
circuit for a piece of 
beef jerky. 



Thoughts on Becoming and Being an Analog Circuit Designer 

your beautiful oscilloscope, spot- weld it to some part of your body so 
that it is not borrowed without your knowledge. 

I am an absolute hard-core fan of Tektronix test equipment. Tektromx 
oscilloscopes (the most important item) are available with a wonderful 
user interface and provide extremely high performance plus real versatil- 
ity. The only problem is that they don't make that kind any more. 

In recent years, there has been a trend toward computer-CiDntrolled, 
menu-driven test instruments, rather than instruments that use a dedicated 
switch or knob for each function (so-called "knob-driven" instruments). 
In most cases, the push for menu-driven test instruments has an economic 
basis— they are simply cheaper to build or provide more features for the 
same price. However, there are practical drawbacks to that approach in 
many cases. A common example, familiar to anyone who has ever used 
an oscilloscope, is the frequent need to ground the input of a vertical 
channel to establish a "zero" reference. With a knob-driven instrument, 
a simple movement of the index finger and thumb will suffice. With a 
menu-driven instrument, one often has to fumble through sevCatal nested 
menus. This really sucks, and I think it is because they are starting to let 
MBAs design oscilloscopes. (I suppose one possible benefit of this is that 
soon 'scopes will have a built-in mode that tells you when to refinance 
your mortgage!) 

Grounding a vertical channel's input is something you need to do 
often, and it is quite analogous to something familiar even to digital engi- 
neers, like going to the bathroom. You simply wouldn't want to scroll 
through a bunch of menus during your mad dash to the bathrodm after 
the consumption of a bad burrito! There are several similar annoyances 
that can crop up when using menu-driven instruments (how about ten 
keystrokes to get a simple sine wave out of a signal generator?!). 

To be fair, menu-driven instruments do have advantages. However, 
since I am not a big fan of them, I'll conveniently omit them here.^ ' It 
always pisses me off to watch students hitting the "auto setup'* button on 
the digital 'scopes in our teaching lab and assuming it is doing the right 
thing for them every time (not!). If we didn't force them to, most of them 
would not even explore the other functions! Advertisements for these 
new instruments often brag that they have a more "analog-like feel" (as 
opposed to what, a "primordial slime ooze feel"?). Let's get real here . . . 
at least in part, this is just another incam^ion of the old engineering say- 
ing, "If you can't fix it, make it a feature." Since when was a "more 
chocolate-like taste" a real key reason to buy brown sludge instead of 
chocolate? 



13. One of the key advantages is that they can help us lure would-be engineers into the lab The type 
of EE student who doesn't like hands-on hardware engineering (you know, the ones who end up 
working for Microsloth) can be attracted by the nice menus long enough to actuiJly see how 
much fun electronics can be. 

14. At this point, I will admit that our VCR does blink *'12:(X)," but I hear there will be an 
'*auto-setup" mode on new ones! I had to fiddle with it for hours to get it to blink ^12:00-" 



50 



GregoryT. A. Kovacs 





I am sad to report that knob-driven analog test instruments are becoming 
more dii¥icult to get. I also have to admit that performance is improving 
while relative prices are dropping^ so "user-friendly" instruments aren't all 
that bad. Students take note: at least try to check out instmments with 
knobs, in between pressing "auto-setup" and **help*' keys! A great place to 
find this stuff is at your friendly neighborhood university (weMl never sur- 
render!), local '*ham radio*' swap meets, and companies that specialize in 
used test equipment. Also, remember to be nice to your oscilloscope! What 
you look like to that faithftil piece of test gear is shown in Figure 5^, 



Figure 5-4. 

What you look like 
to your oscilloscope 
(yuk!), Actually, this 
is what Jim 
Williams looks like 
to his oscilloscope. 
You probably won't 
look that silly. 



What Does My Wife Think about All of This? 



This section was written by my wife, Laurel Beth Joyce, the pride of 
Mars, PA.^^ It is added to provide an extra sense of realism and to prepare 



i 5. 1 am nor making this up. This is because I don't need to. Western PA has tons of great names of 
towns» like Beaver, Moon* etc., as well as great names for public utilities, like "Peoples' Natural 
Gas " Naturally, nobody from there thinks any of this is funny. 



Thoughts on Becoming and Being an Analog Circuit Designer 

a would-be analog circuit designer for the impact this career choice has 
on one's home lifeJ^ 

If your S.O. is an analog designer, your relationship will be much hap- 
pier once you come to understand and accept some of the basic differ- 
ences between analog circuit designers and normal people. 

1 . Analog circuit designers consider beer one of the major food 
groups and an essential hacking tool. (See "Things You Need to 
Survive as a *Re£d' Analog Designer.") To avoid major alterca- 
tions, be sure there's always beer in the hou^. 

Fortunately, my husband's students signed him up for a Beer-of-the 
Month club. Each month the UPS lady drops a big box of beer on our 
doorstep, putting him in hacker heaven and saving me many trips to the 
beer store. 

2. Circuit designers don't tell time in the same way that tl^ rest of 
us do. Unfortunately, I still haven't figured out the exact formula 
for converting circuit design time into regul^ time. 

For example, let's say my husband is in the middle of a hacking proj- 
ect at work and he calls to tell me that he's going to head home in about 
half an hour. If he's alone and I know he's working on a project that 
doesn't require an oscilloscope, I simply multiply the time by two. If 
there is an oscilloscope involved, I multiply by three . If he' s got any cir- 
cuit design friends with him, I generally add at least 40 minutes per 
friend if they're not drinking beer and an extra 2 hours per friend if they 
are. I believe the beer effect is nonlinear My current empirical formula 
for computing circuit design time in minutes is thus: 

t,, = (2 + N,,^Jt + (40+120 

^brewski) ^friends 

where N^copes is the number of oscilloscopes present, kbrewski is the linear 
approximation for the nonlinear beer effect (taken to be one, but can be 
replaced by a suitable time-dependent nonlinearity) and Nf^ends is the 
number of circuit design friends present. 

My calculations are rarely perfect, so I'm pretty sure there are some 
other variables involved. It may have something to do with the number of 
op amps in the project, but since I'm still trying to figure out what aH op 
amp is, I haven't quite determined how that should factor into the formula. 

My suspicion is that this formula varies slighdy among hackers, but 
you're probably safe to use this as a starting point for deriving your own 
formula. 

3. Circuit designers have an interesting concept of economics. Last 
weekend we wandered down the breakfast cereal aisle of out local 



16. The opinions and/or other crap written by my wife are completely her fault and do not reflect the 
opinions and/or other crap of Stanford University or myself in any way. 



52 



Gregory t A. Kovacs 



grocery and my husband was astounded that the big box of Cap'n 
Crunch cost $4.58. He considered it so expensive, he wanted to 
put it back on the shelf. 

In contrast, he tells me that $2,000 is a bargain for a 20-year-old, used 
oscilloscope that only smokes a little bit and will only require one or two 
weekends to fix up. And $1,000 is a great deal on a 'scope that doesn't 
work at all, because it can be cannibalized for parts to repair the 'scopes 
that smoke comes out of (assuming that it has enough parts left that never 
smoked). 

4. When an analog circuit designer brings home a new piece of 
equipment, the S O. becomes invisible for several hours. 

I used to get jealous every time a new 'scope or signal generator came 
into the house. He'd burst in the door all breathless and say, "Hi, Laurel, 
look what I found today* Isn't she beautiful? I'm just going to take her 
upstairs for a few minutes." The two would disappear into the lab and I'd 
hear lots of cooing and giddy chatter that went on until daybreak. It was 
as if my S.O. was bringing home his mistress and dashing up to our bed- 
room right under my nose. 

If the dog or I went into the room, he wouldn't even notice us. I could 
tell him that beer had just been outlawed in the United States or the dog 
could vomit on his shoes. He'd just say, *T11 be with you in a minute," 
and go back to grinning and twiddling the knobs of his new toy. 

When you realize it's no use being jealous and that you'll never be 
able to compete with these machines (unless you want to turn to the folks 
at Tdctronix for fashion advice aijd get some clothes in that particular 
shade of blue, some 'scope knob earrings and some WD-40 cologne), 
you can actually have some fun when your S.O. is in this condition. If 
you like to watch TV, you've got the remote control to yourself for a few 
hours. If you have friends that your S.O. caii't stand, invite them over for 
aparty. If you're angry with your S.O. you can stand there and say nasty 
things ('Tou solder-sucking slimeball!"), get all the anger out of your 
system, and he'll remain totally oblivious. Be creative! 

I was miserable before I learned that these basic differences and quirks 
are characteristic of most analog circuit designers, not just my husband. 
When I finally understood that they're simply a different species, my 
bills for psychoanalysis decreased significantly. 

There are a couple of other things that help, too. First, ask all of your 
relatives to move to towns where there are used test equipment shops or 
frequent swap meets. If you don't, you may never see them again. It took 
six years for my husband to meet my Aunt Gertrude, but as soon as he 
found out that Crazy Egbert's World of 'Scopes was only 12 miles from 
her house, we were on an airplane — "Because I feel terrible that it has 
taken me so long to meet your aunt" — within 24 hours. 

And, when all else fails, you may have to resort to the spouse align- 
ment unit (SAU). Mine is a wooden rolling pin (shown in Figure 5-5), 



53 



Thoughts on Becoming and Being an Analog Circuit Designer 



RgureS^. 

The pride of Mars, 
PA, with her spouse 
aiignment unit 
(SAU). 




but I hear a baseball bat or cast-iron skillet works just as well. The SAU 
comes in handy, for example, when you Ye hosting a large dinner party, 
all the guests have arrived and are waiting for their meal, and your analog 
circuit designer has said heMl join the party **in just a minute" for the past 
two hours. In this situation you should quietly hide the SAU up your 
sleeve, excuse yourself while flashing a charming smile at your guests, 
waltz into the lab, yank the plug on the soldering iron and strike a threat- 
ening pose with the SAU. 

It's kind of like training a dog with a rolled-up newspaper — you only 
have to use it once. After that, the sight of the unit or the threat that 
you're in the mood to do some baking will yield the desired response. 

Conclusion 

I hope this chapter has given you some sense of what you need to learn 
and obtain to become an analog circuit designer, as well as some of the 
emotional challenges in store for you. It would be great if you considered 
it as an alternative to the digital- or software-based engineering drudgery 
that you are statistically likely to end up doing. There may yet be some 
burnt resistors and oscillations in your future! 



Richard p. Feymnan 



6. Cargo Cult Science' 



During the Middle Ages there were all kinds of crazy ideas, such as that 
a piece of rhinoceros horn would increase potency. Then a method was 
discovered for separating the ideas — which was to try one to see if it 
worked, and if it didn't work, to eliminate it. This method became orga- 
nized, of course, into science. And it developed very well, so that we are 
now in the scientific age. It is such a scientific age, in fact, that we have 
difficulty in understanding how witch doctors could ever have existed, 
when nothing that they proposed ever really worked — or very little of 
it did. 

But even today I meet lots of people who sooner or later get me into a 
conversation about UFOs, or astrology, or some form of mysticism, ex- 
panded consciousness, new type of awareness, ESP, and so forth. And 
I've concluded that it's not a scientific world. 

Most people believe so many wonderful things that I decided to inves- 
tigate why they did. And what has been referred to as my curiosity for 
investigation has landed me in a difficulty where I found so much junk 
that I'm overwhelmed. First I started out by investigating various ideas of 
mysticism, and mystic experiences. I went into isolation tanks and got 
many hours of hallucinations, so I know something about that. Then I 
went to Esalen, which is a hotbed of this kind of thought (it's a wonderful 
place; you should go visit there). Then I became overwhelmed. I didn't 
realize how much there was. 

At Esalen there are some large baths fed by hot springs situated on a 
ledge about thirty feet above the ocean. One of my most pleasurable ex- 
periences has been to sit in one of those baths and watch the waves crash- 
ing onto the rocky shore below, to gaze into the clear blue sky above, and 
to study a beautiful nude as she quietly appears and settles into the bath 
with me. 

One time I sat down in a bath where there was a beautiful girl sitting 
with a guy who didn't seem to know her. Right away I began thinking, 
*'Gee! How am I gonna get started talking to this beautifol nude babe?" 

I'm trying to figure out what to say, when the guy says to her, "I'm, 
uh, studying massage. Could I practice on you?" 



Adapted from the Cal Tech commencement address given in 1974. 



55 



Cargo Cult Science 



"Sure " she says. They get out of the bath and she lies down on a mas- 
sage table nearby. 

I think to myself, "What a nifty line! I can never think of anything like 
that!" He starts to rub her big toe. "I think I feel it," he says. "I feel a kind 
of dent — is that the pituitary?" 

I blurt out, "You're a helluva long way from the pituitary, man!" 

They looked at me, horrified— I had blown my cover — and said, "It's 
reflexology!" 

I quickly closed my eyes and appeared to be meditating. 

That's just an example of the kind of things that overwhelmme. I also 
looked into extrasensory perception and PSI phenomena, and the latest 
craze there was Uri Geller, a man who is supposed to be able to bend 
keys by rubbing them with his finger. So I went to his hotel room, on his 
invitation, to see a demonstration of both mindreading and bending keys. 
He didn't do any mindreading that succeeded; nobody can read my mind, 
I guess. And my boy held a key and Geller rubbed it, and nothing hap- 
pened. Then he told us it works better under water, and so you can pic- 
ture all of us standing in the bathroom with the water turned on and the 
key under it, and him rubbing the key with his finger. Nothing happened. 
So I was unable to investigate that phenomenon. 

But then I began to think, what else is there that we believe? (And I 
thought then about the witch doctors, and how easy it would have been to 
check on them by noticing that nothing really worked.) So I found things 
that even more people believe, such as that we have some knowledge of 
how to educate. There are big schools of reading methods and mathemat- 
ics methods, and so forth, but if you notice, you'll see the reading scores 
keep going down — or hardly going up — in spite of the fact that we con- 
tinually use these same people to improve the methods. There's a witch 
doctor remedy that doesn't work. It ought to be looked into; how do they 
know that their method should work? Another example is how to treat 
criminals. We obviously have made no progress — lots of theory, but no 
progress — in decreasing the amount of crime by the method that we use 
to handle criminals. 

Yet these things are said to be scientific. We study them. And I think 
ordinary people with commonsense ideas are intimidated by this pseudo- 
science. A teacher who has some good idea of how to teach her children 
to read is forced by the school system to do it some other way — or is 
even fooled by the school system into thinking that her method is not 
necessarily a good one. Or a parent of bad boys, after disciplining them 
in one way or another, feels guilty for the rest of her life because she 
didn't do "the right thing," according to the experts. 

So we really ought to look into theories that don't work, and science 
that isn't science. 

I think the educational and psychological studies 1 mentioned are ex- 
amples of what I would like to call cargo cult science. In the South Seas 
there is a cargo cult of people. During the war they saw airplanes land 



56 



Richard p. Feynman 



with lots of good materials, and they want the same thing to happen now. 
So they've arranged to make things like runways, to put fires along the 
sides of the runways, to make a wooden hut for a man to sit in, with two 
wooden pieces on his head like headphones and bars of bamboo sticking 
out like antennas — he's the controller — and they wait for the airplanes to 
land. They're doing everything right. The form is perfect. It looks exactly 
the way it locked before. But it doesn't work. No airplanes land. So I call 
these things cargo cult science, because they follow all the apparent pre- 
cepts and forms of scientific investigation, but they're missing something 
essential, because the planes don't land. 

Now it behooves me, of course, to tell you what they're missing. But it 
would be just about as difficult to explain to the South Sea Islanders how 
they have to arrange things so that they get some wealth in their system. 
It is not something simple like telling them how to improve the shapes of 
the earphones. But there is one feature I notice that is generally missing 
in cargo cult science. That is the idea that we all hope you have learned 
in studying science in school — we never explicitly say what this is, but 
just hope that you catch on by all the examples of scientific investigation. 
It is interesting, therefore, to bring it out now and speak of it explicitly. 
It's a kind of scientific integrity, a principle of scientific thought that cor- 
responds to a kind of utter honesty — a kind of leaning over backwards. 
For example, if you're doing an experiment, you should report everything 
that you think might make it invaUd — ^not only what you think is right 
abont it: other causes that could possibly explain your results; and things 
you thought of that you've eliminated by some other experiment, and 
how they worked — to make sure the other fellow can tell they have been 
eliminated. 

Details that could throw doubt on your interpretation must be given, if 
you know them. You must do the best you can — if you know anything at 
all wrong, or possibly wrong — to explain it. If you make a theory, for 
example, and advertise it, or put it out, then you must also put down all 
the facts that disagree with it, as well as those thdH agree with it. There is 
also a more subtle problem. When you have put a lot of ideas together to 
make an elaborate theory, you want to make sure, when explaining what 
it fits, that those things it fits are not just the things that gave you the idea 
for the theory; but that the finished theory makes something else come 
out right, in addition. 

In summary, the idea is to try to give all of the information to help 
others to judge the value of your contribution; not just the information 
that leads to judgment in one particular direction or another. 

The easiest way to explain this idea is to contrast it, for example, with 
advertising. Last night I heard that Wesson oil doesn't soak through 
food. Well, that's true. It's not dishonest; but the thing I'm talking about 
is not just a matter of not being dishonest, it's a matter of scientific in- 
tegrity, which is another level. The fact that should be added to that ad- 
vertising statement is that no oils soak through food, if operated at a 



57 



Cargo Cult Science 



certain temperature. If operated at another temperature, they all will- 
including Wesson oil. So it's the implication which has been conveyed, 
not the fact, which is true, and the difference is what we have to deal with. 

We've learned from experience that the truth will come out. Other 
experimenters will repeat your experiment and find out whether you were 
wrong or right. Nature's phenomena will agree or they'll disagree with 
your theory. And, although you may gain some temporary fame and ex- 
citement, you will not gain a good reputation as a scientist if you haven't 
tried to be very careful in this kind of work. And it's this type of integrity, 
this kind of care not to fool yourself, that is missing to a large extent in 
much of the research in cargo cult science. 

A great deal of their difficulty is, of course, the difficulty of the subject 
and the inapplicability of the scientific method to the subject. Neverthe- 
less, it should be remarked that this is not the only difficulty. That's why 
the planes don't land— but they don't land. 

We have learned a lot from experience about how to handle some of 
the ways we fool ourselves. One example: Millikan measured the charge 
on an electron by an experiment with falling oil drops, and got an answer 
which we now know not to be quite right. It's a little bit off, because he 
had the incorrect value for the viscosity of air. It's interesting lo look at 
the history of measurements of the charge of the electron, after Millikan. 
If you plot them as a function of time, you find that one is a little bigger 
than Millikan' s, and the next one's a httle bit bigger than that, and the 
next one's a little bit bigger than that, until finally they settle down to a 
number which is higher. 

Why didn't they discover that the new number was higher right away? 
It's a thing that scientists are ashamed of — ^this history — because it's 
apparent that people did things like this: When they got a number that 
was too high above Millikan's, they thought something must be wrong — 
and they would look for and find a reason why something might be 
wrong. When they got a number closer to Millikan's value they didn't 
look so hard. And so they eliminated the numbers that were too far off, 
and did other things like that. We've learned those tricks nowadays, and 
now we don't have that kind of a disease. 

But this long history of learning how to not fool ourselves — of having 
utter scientific integrity — is, Fm sorry to say, something that we haven't 
specifically included in any particular course that I know of. We just hope 
you've caught on by osmosis. 

The first principle is that you must not fool yourself— and you are the 
easiest person to fool. So you have to be very careful about that. After 
you've not fooled yourself, it's easy not to fool other scientists. You just 
have to be honest in a conventional way after that, 

I would like to add something that's not essential to the science, but 
something I kind of believe, which is that you should not fool the lay- 
man when you're talking as a scientist. I am not trying to tell you what 
to do about cheating on your wife, or fooling your girlfriend, or some- 
thing like that, when you're not trying to be a scientist, but just trying to 



58 



Richard RFeynman 



be an ordinary human being. We'll leave those problems up to you and 
your rabbi. Fm talking about a specific, extra type of integrity that is not 
lying, but bending over backwards to show how you're maybe wrong, 
that you ought to have when acting as a scientist. And this is our respon- 
sibility as scientists, certainly to other scientists, and I think to laymen. 

For example, I was a little surprised when I was talking to a friend 
who was going to go on the radio. He does work on cosmology and as- 
tronomy, and he wondered how he would explain what the applications 
of this work were. "Well," I said, "there aren't any." He said, "Yes, but 
then we won't get support for more research of this kind." I think that's 
kind of dishonest. If you're representing yourself as a scientist, then you 
should explain to the layman what you're doing — and if they don't want 
to support you under those circumstances, then that's their decision. 

One example of the principle is this: If you've made up your mind to 
test a theoty, or you want to explain some idea, you should always decide 
to publish it whichever way it comes out. If we only publish results of a 
certain kind, we cm make the argument look good. We must publish both 
kinds of results . 

I say that's also important in giving certain types of government ad- 
vice. Supposing a senator asked you for advice about whether drilling a 
hole should be done in his state; and you decide it would be better in 
some other state. If you don't publish such a result, it seems to me you're 
not giving scientific advice. You're being used. If your answer happens to 
come out in the direction the goverament or the politicians like, they can 
use it as an argument in their favor; if it comes out the otho* way, they 
don't publish it at all. That's not giving scientific advice. 

Other kinds of errors are more characteristic of poor science. When I 
was at Cornell, I often talked to the people in the psychology department. 
One of the students told me she wanted to do an experiment that went 
something like this — it had been found by others that under certain cir- 
cumstances, X, rats did sometiiing, A. She was curious as to whether, if 
she changed the circumstances to Y, they would still do A. So her pro- 
posal was to do the experiment under circumstances Y and see if they 
still did A. 

I explained to her that it was necessary first to repeat in her laboratory 
the experiment of the other person— to do it under condition X to see if 
she could also get result A, and then change to Y and see if A changed. 
Then she would know that the real difference was the thing she thought 
she had under control. 

She was very delighted with this new idea, and went to her professor. 
And his reply was, no, you cannot do that, because the experiment has 
already been done and you would be wasting time. This was in about 
1947 or so, and it seems to have been the general policy then to not try to 
repeat psychological experiments, but only to change the conditions and 
see what happens. 

Nowadays there's a certain danger of the same thing happening, even 
in the famous field of physics. I was shocked to hear of an experiment 



59 



Cargo Cult Science 



done at the big accelerator at the National Accelerator Laboratory, where 
a person used deuterium. In order to compare his heavy hydrogen results 
to what might happen with light hydrogen, he had to use data from some- 
one else's experiment on light hydrogen, which was done on different 
apparatus. When asked why, he said it was because he couldn't get time 
on the program (because there's so little time and it's such expensive 
apparatus) to do the experiment with light hydrogen on this apparatus 
because there wouldn't be any new result. And so the men in charge of 
programs at NAL are so anxious for new results, in order to get more 
money to keep the thing going for public relations purposes, tti^ are 
destroying — possibly — the value of the experiments themselves, which is 
the whole purpose of the thing. It is often hard for the experimenters 
there to complete their work as their scientific integrity demands. 

All experiments in psychology are not of this type, however. For ex- 
ample, there have been many experiments running rats through all kinds 
of mazes, and so on — with little clear result. But in 1937 a man named 
Young did a very interesting one. He had a long corridor with doors all 
along one side where the rats came in, and doors along the other side 
where the food was. He wanted to see if he could train the rats to go in at 
the third door down from where he started them off. No. The rats went 
immediately to the door where the food had been the time befOTe. 

The question was, how did the rats know because the corridor was so 
beautifully built and so uniform that this was the same door as before? 
Obviously there was something about the door that was diflGKnent from 
the other doors. So he painted the doors very carefully, arranging the 
textures on the faces of the doors exactly the same. Still the rats could 
tell. Then he thought maybe the rats were smelling the food, so he used 
chemicals to change the smell after each run. Still the rats could tell. 
Then he realized the rats might be able to tell by seeing the lights and the 
arrangement in the laboratory like any commonsense person. So he cov- 
ered the corridor^ and still the rats could tell 

He finally found that they could tell by the way the floor sounded 
when they ran over it. And he could only fix that by putting his corridor 
in sand. So he covered one after another of all possible clues and finally 
was able to fool the rats so that they had to learn to go in the third door If 
he relaxed any of his conditions, the rats could tell. 

Now, from a scientific standpoint, that is an A-number-one experi- 
ment. That is the experiment that makes rat-running experiments sensi- 
ble, because it uncovers the clues that the rat is really using— not what 
you think it's using. And that is the experiment that tells exactly what 
conditions you have to use in order to be careful and control every thing 
in an experiment with rat-running. 

I looked into the subsequent history of this research. The next experi- 
ment, and the one after that, never referred to Mr. Young. They never 
used any of his criteria of putting the corridor on sand, or being very 
careful. They just went right on running rats in the same old way, ^d 
paid no attention to the great discoveries of Mr. Young, and his papers are 



60 



Richard R F^nman 



not referred to, because he didn't discover anything about the rats. In 
fact, he discovered all the things you have to do to discover something 
about rats. But not paying attention to experiments like that is a charac- 
teristic of cargo cult science. 

Another example is the ESP experiments of Mr. Rhine, and other peo- 
ple. As various people have made criticisms — and they themselves have 
made critieisims of their own experiments— they improve the techniques 
so that the effects are smaller, and smaller, and smaller until they gradu- 
ally disappeiir. All the parapsychologists are looking for some experiment 
that can be repeated— that you can do again and get the san^ effect — 
statistically, even. They run a million rats — no, it's people this time — 
Ihey do a lot of things and get a certain statistical effect. Next time they 
try it they don't get it any more. And now you find a man saying that it is 
an irrelevant demand to expect a repeatable experiment. This is science? 

This man also speaks about a new institution, in a talk in which he was 
resigning as Director of the Institute of Parapsychology. And, in telling 
people what to do next, he says that one of the things they have to do is 
be sure they only train students who have shown their ability to get PSI 
results to an acceptable extent- — ^not to waste their time on those ambi- 
tious and interested students who get only chance results. It is very dan- 
gerous to have such a policy in teaching — ^to teach students only how to 
get certain results, rather than how to do an experiment with scientific 
integrity. 

So I have just one wish for you— the good luck to be somewhere 
where you are free to maintain the kind of integrity I have described, and 
where you do not feel forced by a need to maintain your position in the 
organization, or financial support, or so on, to lose your integrity. May 
you have that freedom. 



61 



This page intentionally left blank 



Part Two 

Making It Work 



Five authors in this section give guided tours into what it takes to go 
from concept to a completed, functional circuit. Steve Roach shows how 
monstrously complex a "simple" voltage divider can become when it's 
an oscilloscope input attenuator. Bill Gross gives an eye-opening trip 
through the development process of an analog integrated circuit, with 
special emphasis on how tradeoffs must be dealt with, James Bryant ex- 
plores a fast, flexible way to breadboard analog circuits which is usable 
from DG to high frequency. A true pioneer in wideband oscilloscope 
design, Carl Battjes, details the intricacies of T-coil design, an enabling 
technology for wideband oscilloscopes. In the section's finale, Jim 
Williams writes about how hard it can be to get your arms around just 
what the problem is. Imagine taking almost a year to find the right way 
to turn on a light bulb! 



63 



This page intentionally left blank 



Steve Roach 



7. Signal Conditioning in Oscilloscopes 

and the Spirit of Invention 



The Spirit of Invention 

When I was a child my grandfather routinely asked me if I was going to 
be an engineer when I grew up. Since some of my great-uncles worked 
on the railroads, I sincerely thought he wanted me to follow in their foot- 
steps. My grandfather died before I clarified exactly what kind of engi- 
neer he hoped I would become, but I think he would approve of my 
interpretation. 

I still wasn't sure what an engineer was when I discovered I wanted to 
be an inventor. I truly pictured myself alone in my basement toiling on 
the important but neglected problems of humanity. Seeking help, I joined 
the Rocky Mountain Inventors' Congress. They held a conference on 
invention where I met men carrying whole suitcases filled with clever 
little mechanical devices. Many of these guys were disgruntled and 
cranky because the world didn't appreciate their contributions. One of 
the speakers, a very successful independent inventor, told of a bankrupt 
widow whose husband had worked twenty years in isolation and secrecy 
inventing a mechanical tomato peeler. The tomato peeler had consumed 
the family savings, and the widow had asked the speaker to salvage the 
device. With sadness the speaker related the necessity of informing her 
that tomatoes were peeled in industrial quantities with sulfuric acid. 
Apparently the inventor had been too narrowly focused to realize that 
in some cases molecules are more powerful than machines. 

I didn't want to become disgruntled, cranky, or isolated and I didn't 
even own a basement. So I went to engineering school and adopted a 
much easier approach to inventing. I now design products for companies 
with such basic comforts as R&D budgets, support staff, and manufactur- 
ing operations. Along the way I have discovered many ways of nurturing 
inventiveness. Here are some techniques that seem to work: 

Give yourself time to invent. If necessary, steal this time from the un- 
ending rote tasks that your employer so readily recognizes and rewards. I 
try to work on things that have nothing to do with a particular product, 
have no schedule, and have no one expecting results. I spend time on 
highly tangential ideas that have little hope for success. I can fail again 
and again in this daydream domain with no sense of loss. 



65 



Signal Conditioning in Oscilloscopes and the Spirit of Invention 

Get excited. Enjoy the thrilling early hours of a new idea. Stay up all 
night, lose sleep, and neglect your responsibilities. Freely explore tan- 
gents to your new idea. Digress fearlessly and entertain the absurd. 
Invent in the morning or whenever you are most energetic. Save your 
"real" work for when you are tired. 

Master the fundamentals of your field. The most original and creative 
engineers I have known have an astonishing command of undergraduate- 
level engineering. Invention in technology almost always stems from the 
novel application of elementary principles. Mastery of fundamentals al- 
lows you to consider, discard, and develop numerous ideas quickly, accu- 
rately, and fairly. 1 believe so much in this concept that I have begun 
taking undergraduate classes over again and paying very careful attention. 

Honestly evaluate the utility of your new idea at the right timie: late 
enough not to cut off explorations of alternatives and wild notions, but 
early enough that your creativity doesn't go stale. In this stage you must 
ask the hardest questions: "Is this new thing useful to anyone else? Ex- 
actly where and how is it useful? Is it really a better solution or just a 
clever configuration of parts?" Even if you discover that your creation 
has no apparent utility, savor the fun you had exploring it and be thMikful 
that you don't have the very hard work of developing it. 

Creativity is not a competitive process. It is sad that we engineers are 
so inculcated with the competitive approach that we use it even privately. 
You must suspend this internal competition because almost all of your 
new ideas will faiL This is a fact, but it doesn't detract a bit from the fun 
of inventing. 

Now it's time to get on to a very old and interesting analog design 
problem where there is still a great deal of room for invention. 

Requirements for Signal Conditioning 
in Oscitloscopes 

Most of my tenure as an electrical engineer has been spent designing 
analog subsystems of digital oscilloscopes. A digital oscilloscope is a 
rather pure and wholesome microcosm of signal processing and measure- 
ment, but at the signal inputs the instrument meets the inhospitable real 
world. The input signal-conditioning electronics, sometimes referred 
to as the "front-end" of the instrument, includes the attenuators, high- 
impedance buffer, and pre-amplifier. Figure 7-1 depicts a typical front- 
end and is annotated with some of the performance requirements. 

The combination of requirements makes the design of an oscilloscope 
front-end very difficult. The front-end of a 500MHz oscilloscope devel- 
ops nearly IGHz of bandwidth and must have a very clean step response. 
It operates at this bandwidth with a IMQ input resistance! No significant 
resonances are allowed out to 5GHz or so (where everything wants to 
resonate). Because we must maintain high input resistance and low ca- 
pacitance, transmission lines (the usual method of handling microwave 



66 



St^ Roach 



instrument 
•ilWK2*0.2% ll lOpF 

* 50QMHZ ban^ 

* Gatjnfl4rtrie«$ <0.5% 

* Low fefleetibn fn SQQ mode 
•amVto40Vfullscate 

* ±400V overvaltage toferaricfe 

* 251^1/ ESD safe 

* 6nVNHz avg. noise density 

* 1 mVpp broadband noise 



Attenuator 



' Constant input impedance for 
all attenuation steps 
' High voltage (>40dV} switches 
• High impedance with microwave 
bandwidth 

Protection Diodes 

> Diodes carry amps ofESD 
current vMth <1ns risetlrne 

> <1pF total diode capacitance 



Input 



ESP Protection 
(Spark gap) 



50Q 



High Impedance 
Switched 
Attenuator 



ma 




Attenuation 
Control 



Pre-amplifier 

• 10k£2 j{ 2pF input impedance 

• Twice the BW of the instrument 
(>1GHzfor a SOOMHz scope!) 

• Continuously variable gain 
from 1 to 50 

• 7(X2 output resistance 

Pre-ampfifier 

^ ToA/D 
Converter 

** To Trigger 
System 



impedance 
Converter 



Impedance Converter 



>10CMUIQ input resistance 

• <1pF input capacitance 

• 5CX1 output resistance 

• Twice the BW of the instrument 
{>1 GHz for a 500MHz scope! ) 

■ DC perfornnance of a precision opamp 



signals) are not allowed! The designer's only defense is to keep the physi- 
cal dimensions of the circuit very small To obtain the 1 GHz bandwidth 
we must use microwave components. Microwave transistors and diodes 
are typically very delicate, yet the front-end has to withstand ±400V ex- 
cursions and high-voltage electrostatic discharges. Perhaps the most diffi- 
cult requirement is high gain flatness from DC to a significant fraction of 
full bandwidth. 

A solid grasp of the relationships between the frequency and time 
domains is essential for the mastery of these design challenges. In the 
following I will present several examples illustrating the intuitive connec 
tions between the frequency magnitude and step responses. 

llmFr^fyincyamlTi 

Oscilloscopes are specified at only two frequencies: DC and the -3dB 
point. Worse, the manufacturers usually state the vertical accuracy at DC 
only, as if an oscilloscope were a voltmeter! Why is a time domain mea- 
suring device specified in the frequency domain? The reason is that band- 
width measurements are traceable to international standards, whereas it is 
extremely difficult to generate an impulse or step waveform with known 
properties (Andrews 1983, Rush 1990). 

Regardless of how oscilloscopes are specified, in actual practice oscil- 
loscope designers concern themselves almost exclusively with the step 
response. There^e several reasons for focusing on the step response: 
(1) a good step response is what the users really need in a time domain 
instrument, (2) the step response conveys at a glance information about 
a very wide band of frequencies, (3) with practice you can learn to intu- 
itively relate the step response to the frequency response, and (4) the step 

67 



Figure 7-1, 

Annotated diagranfi 
of an oscilloscope 
front-end, showing 
specifications and 
requirements at 
each stage. 



Signal Conditioning in Oscilloscopes and the Spirit of Invention 



Figure 7-2. 

Definition of terms 
and relationships 
between the 
frequency magni- 
tude and step 
responses. 



response will be used by your competitors to find your weaknesses and 
attack your product. 

Figure 7-2 defines the terms of the frequency and step responses and 
shows the meaning of flatness error. Response flatness is a qualitative 
notion that refers roughly to gain errors not associated with the poles that 
determine the cutoff frequency, or equivalently to step response errors 
following the initial transition. To assess flatness we generally ignore 
peaking of the magnitude near the 3dB frequency. We also ignore short- 
term ringing caused by the initial transition in the step response. 

Figure 7-2 illustrates the rough correspondence between^ high- 
frequency portions of the magnitude response and the early events in the 
step response. Similarly, disturbances in the magnitude response at low 
frequencies generate long-term flatness problems in the step response 



Magnitude 
Response (dB) 




Resonances and 
transmission line 
reflections 



Frequency (Hz) 



Preshoot 



68 



Steve Roach 



(Kamath 1974). Thus the step response contains information about a very 
wide band of frequencies, when observed over a long enough time pe- 
riod. For example, looking at the first ten nanoseconds (ns) of the step 
conveys frequency domain information from the upper bandwidth of the 
instrument down to approximately l/(10ns) or lOOMHz. 

Figure 7-3 shows an RC circuit that effectively models most sources 
of flatness errors. Even unusual sources of flatness errors, such as dielec- 
tric absorption and thermal transients in transistors, can be understood 
with similar RC circuit models. The attenuator and impedance converter 
generally behave like series and parallel combinaticms of simple RC cir- 
cuits. Circuits of this form often create flatness problems at low frequen- 
cies because of the high resistances in an oscilloscope front-end. In 
contrast, the high-frequency problems are frequently the result of the 
innun^rable tiny inductors and inadvertent transmission lines introduced 
in the physical construction of the circuit. Notice how in Figure 7-3 the 
reciprocal nature of the frequency and step responses is well represented. 



Oscilloscopes by convention and tradition have 1M£1 inputs with just a 
few picofarads of input capacitance. The IMQ input resistance largely 
determines the attenuation factor of passive probes, and therefore must 
be accurate and stable. To maintain the accuracy of the input resistsuice, 
the oscilloscope incorporates a very high input impedance unity gain 
buffer (Figure 7-1). ITiis buffer, sometimes called an "impedance con- 
verter,'* presents more than 100MS2 at its input while providing a low- 
impedance, approximately 50fl output to cWve the pre-amp. In a 
500MHz oscilloscope the impedance converter may have IGHz of band- 
width and very carefully controlled time domain response. This section 



Figure 7-3. 

A simple circuit that 
models most 
sources of ftelness 
errors. 

too big 





Vo(t)/V((t) too big 




step Response 



69 



Signal Conditioning in Oscilloscopes and the Spirit of Invention 



shows one way in which these and the many additional requirements of 
Figure 7-1 can be met (Rush 1986). 

A silicon field effect transistor (FET) acting as a source fbllower is the 
only type of commercially available device suitable for implementing the 
impedance converter For 500MHz instruments, we need a source fol- 
lower with the highest possible transconductance combined with the 
lowest gate-drain capacitance. These parameters are so important in a 
500MHz instrument that oscilloscope designers resort to the use of short- 
channel MOSFETs in spite of their many shortcomings. MOSFETs with 
short channel lengths and thin gate oxide layers develop very high 
transconductance relative to their terminal capacitances. However, they 
suffer from channel length modulation effects which give them undesir- 
ably high source-to-drain or output conductance. MOSFETs are surface 
conduction devices, and the interface states at the gate-to^chaiMel inter- 
face trap charge, generating large amounts of 1/f noise. The 1/f noise can 
contribute as much noise between DC and IMHz as thermal noi^c be- 
tween DC and 500MHz. Finally, the thin oxide layer of the gate - . .ci. up 
very easily in the face of electrostatic discharge. As source followers, 
JFETs outperform MOSFETs in every area but raw speed. In summary, 
short-channel MOSFETs make poor but very fast source followers, and 
we must use a battery of auxiliary circuits to make them function accept- 
ably in the impedance converter. 

Figure 7-4 shows a very basic source follower with the required IMQ 
input resistance. The resistor in the gate stabilizes the FET. Figure 7-5 
shows a linear model of a typical high-frequency, short-channel MOS- 
FET, I prefer this model over the familiar hybrid-ix model because it 
shows at a glance that the output resistance of the source is 1/g^, Figure 
7-6 shows the FET with a surface-mount package model. The tiny capac- 
itors and inductors model the geometric effects of the package and the 
surrounding environment. These tiny components are called "parasitics" 
in honor of their very undesirable presence. Figure 7-7 depicts the para- 
sitics of the very common "0805" surface-mount resistor. This type of 
resistor is often used in front-end circuits built on printed circuit boards- 
Package and circuit board parasitics at the 0.1 pF and InH level seem 
negligibly small, but they dominate circuit performance above 500MHz. 

I Source 
: Follower "P 

Figure 7-4. 

A simple source 
follower using a 
MOSFET. 

1MQ 



Rg 50Q 

-^AA^ — 



r 



P re-amp Load 



Cl2pF 



I 



70 



Steve Roach 



0 6p F : 



Gate 



2.9pF 



Drain 



''ds='^^gds , ^ 
=770Q C^jg 

0.4pF 



Source 



Figure 7-5. 
A linear model of a 
BSD22, a typical 
high-frequency, 
short-channel 
MOSFEt The gate 
current is zero at 
DC because the 
controlled current 
source keeps the 
drain current 
equal to the source 
current. 



In oscilloscope circuits I often remove the ground plane in small patches 
beneath the components to reduce the capacitances. One must be ex- 
tremely careful when removing the ground plane beneath a high-speed 
circuit, because it always increases parasitic inductance. I once turned 
a beautiful 2GHz amplifier into a 400MHz bookend by deleting the 
ground plane and thereby effectively placing large inductors in the 
circuit 



\* — 2.5mm 1 



Drain 

, 0.12 pF 



T 



Subs^F^e 



3.0mm 



Source 















1 









Gate 



Drain 



lead 
0.5 nH 



inter-lead 
capacitance 
ir: 0.04 pF 



inter-lead 
capacitance 



SOT-143 Package 



Gate 



lead 
0.5 nH 



T 



pad 

2pF 




bond wire 
0.5 nH 



Sutistrate 



T 



pad 

0.16pF-j- 



inter-lead 
capacitance 
0.04 pF 



lead r pad 
0.5 nHC 0.12 nH 



Source 



Figum 7-6. 

A MOSFET with SOT-1 43 surface-mount package parasitics. The model includes the effects of mounting on a 
1 .6mm (0.063") thick, six-layer epoxy glass circuit board with a ground plane on the fourth layer from the compo- 
nent side of the board. 



71 



Signal Conditioning in Oscilloscopes and the Spirit of Invention 



1 mm Trace 



0.1 pF 



1 mm Ttkce 




0.6nH 



R 
AAAr 



0.7nH 




aenH 



pad 
0.1 5pF 



pad 
0.1 5pF 



Rgur#7-7. 

A model of an 0805 surface-mount resistor, including a 1mm trace on each end. The model includes the effects 
of mounting on a 1 .6mm (0.063") thick, six-layer epoxy glass circuit board with a ground plane on the fourth layer 
from the cbmponent side of the board. 



Parasitics have such a dominant effect on high-frequency performance 
that 500MHz oscilloscope front-ends are usually built as elrip-and-wire 
hybrids, which have considerably lower parasitics than staiictejrd printed 
circuit construction. Whether on circuit boards or hybrids, the bond 
wires, each with about 0.5 to 1 .OnH inductance, present one of the great- 
est difficulties for high-frequency perfomiance. In the course of (fesign- 
ing high-frequency circuits, one eventually comes to view the circuits 
and layouts as a collection of transmission lines or the lumped approxi- 
mations of transmission lines. I have found this view to be very useftil 
and with practice a highly intuitive mental model. 

Figure 7-8 shows the magnitude and step responses of the simple 
source follower, using the models of Figures 7-5 through 7-7. The band- 
width is good at 1 .IGHz. The rise time is also good at 360ps, and the 1 % 
settling time is under Ins! 

Our simple source follower still has a serious problem. The high 
drain-to-source conductance of the FET forms a voltage divider with the 
source resistance, limiting the gain of the source follower to 0.91. The 
pre-amp could easily make up this gain, but the real issue is temperature 
stability. Both transconductance and output conductance vary with tem- 
perature, albeit in a self-compensating way. We cannot comfortably rely 
on this self-compensation effect to keep the gain stable. The solution is to 
bootstrap the drain, as shown in Figure 7-9. This circuit forces the drain 
and source voltages to track the gate voltage. With bootstrapping, the 
source follower operates at nearly constant current and ne^ly constant 
terminal voltages. Thus bootstrapping keeps the gain high and stable, the 
power dissipation constant, and the distortion low. 

There are many clever ways to implement the bootstrap circuit 
(Kimura 1991). One particularly simple method is shown in Figure 7-10, 
The BF996S dual-gate, depletion-mode MOSFET is intended for use in 
television tuners as an automatic gain controlled amplifier. This device 
acts like two MOSFETs stacked source-to-drain in series. Tlie current 
source shown in Figure 7-10 is typically a straightforward bipolar tran- 
sistor current source implemented with a microwave transistor. An ap- 



72 



Steve Roach 




proximate linear model of the BF996S is shown in Figure 7-11. The 
BF996S comes in a SOT- 143 surface-mount package, with parasitics, as 
shown in Figure 7-6. 

Figure 7-12 shows the frequency and step responses of the boot- 
strapped source follower. The bootstrapping network is AC coupled, so 



Buffer 




% ^ Gate 



Fipie?-^. 

The magnitude and 
step responses of 
the simple source 
foHowef. 



Figure 7-9. 

The boo^iipDed 
source follower. 
Driving the drain 
with the source 
voltage increases 
and stabilizes 
the gain. 



7S 



Signal Conditioning in Oscilloscopes and the Spirit of Invention 



Figure 7-10. 

Bootstrapping the 
drain with a dual- 
gate MOSFET. 



10MQ 
AAAr- 




it does not boost the gain at DC and low frequencies. The response there- 
fore is not very flat, but we can fix it later. From IkHz to lOOMHz the 
gain is greater than 0.985 and therefore highly independent of tempera- 
ture. The 1% settling time is very good at 1.0ns. 

Several problems remain in the bootstrapped source follower of Figure 
7-10. First, the gate has no protection whatever from overvoltages aiid 
electrostatic discharges. Second, the gate-source voltage will vary drasti- 
cally with temperature, causing poor DC stability. Third, the 1/f noise of 
the MOSFET is uncontrolled. The flatness (Figure 7-12) is very poor 
indeed. Finally, the bootstrapped source follower has no ability to handle 
large DC offsets in its input. 

Figure 7-13 introduces one of many ways to build a "two-path" im- 
pedance converter that solves the above problems (Evel 1971, Tektronix 
1972), DC and low frequencies flow through the op amp, whereas high 
frequencies bypass the op amp via CI. At DC and low frequencies, feed- 



Figure 7-11. 

Linear model of the 
BF996S dual-gate, 
depletion MOSFET 



Gate1 



Cgdi 0.3PF 



o Drain 



Cgsi 2.3PF 



Q2 



Q1 

9^,^=1 SmS 



=n 0.5pF 



Source 



74 



Steve Roach 



1*0 1 



G 
a 
I 

n 



~1 

I Mid-band gain is 0.9875 
Low freq. gain is 0,904 



0 

l.OHz 




1.0TH2 



Figure 7-12. 
The magnitude and 
step responses of 
the bootstrapped 
source follower. 



Frequency 



1.0 



G 
a 

i 

n 



Trise = 400ps 



Os 



1.0ns 



2.0ns 



3.0ns 



Time 



back gives the two-path source follower the accuracy of a precision op 
amp. At high frequencies, the signal feeding through CI dominates con- 
trol of gate 1, and the source follower operates open loop. The FET is 
protected by the diodes and the current limiting effects of CI . The 1/f 
noise of the FET is partially controlled by the op amp, and the circuit can 
offset large DC levels at the input with the offset control point shown in 
Hgure 7-13. 

Figure 7-14 shows the flatness details of the two-path impedance con- 
verter. Feedback around the op amp has taken care of the low-frequency 
gain error exhibited by the bootstrapped source follower (Figure 7-12). 
The gain is flat from DC to 80MHz to less than 0. 1 %. The "wiggle" in 
the magnitude response occurs where the low- and high-frequency paths 
cross over. 

There are additional benefits to the two-path approach. It allows us to 
design the high-frequency path through CI and the MOSFET without 
regard to DC accuracy. The DC level of the impedance converter output 
is independent of the input and can be tailored to the needs of the pre- 
amplifier. Although it is not shown in the figures, AC coupling is easily 
implemented by blocking DC to the non-inverting input of the op amp. 



75 



Signal Conditioning in Oscilloscopes and the Spirit of Invention 



"offset* 



Gate 2 



R„ 50Q 

9 

-AA/V 



Source < 




Figure 7-1 3. 

A two-path imped- 
ance converter, rr^ . t ' f t . 1 It . . . ^ 

Thus we avoid putting an AC coupling relay, with all its parasitic effects, 
in the high-frequency path. 

There are drawbacks to the two-path impedance converter. The small 
flatness errors shown in Figure 7-14 never seem to go away, r^ardless 
of the many alternative two-path architectures we try. Also, CI forms a 
capacitive voltage divider with the input capacitance of the source fol- 
lower. Along with the fact that the source follower gain is less than unity, 
this means that the gain of the low-frequency path may not match that 
of the high-frequency path. Component variations cause the flatness to 
vary further. Since the impedance converter is driven by a precision 
high'impedance attenuator, it must have a very well-behavSed input 
impedance that closely resembles a simple RC parallel circuit. In this 
regard the most common problem occurs when the op amp has insuffi- 
cient speed and fails to bootstrap Rl in Figure 7-13 to high enough 
frequencies. 

990m r , 



Figure 7-14. 

Flatness details of 
the two-path 
impedance 
converter. 



G 
a 
f 

n 



980mt--- 
1 .OmHz 



f- 

l.OKHz 
Frequency 



+0.1% error 



-0.1% error 



1: 

100MHz 



76 



The overdrive recovery performance of a two-path amplifier can be 
abysmal. There are two ways in which overdrive problems occur. If a 
signal is large enough to turn on one of the protection diodes, CI charges 
very quickly through the low impedance of the diode (Figure 7~13). As if 
it were not bad enough that the input impedance in overdrive looks like 
270pF, recovery occurs with a time constant of 270pF •4.7Mt2, or 1.3ms! 
Feedback around the op amp actually accelerates recovery somewhat but 
recovery still takes eons compared to the 400ps rise time! Another over- 
drive mechanism is saturation of the source follower. When saturation 
occurs, the op amp integrates the error it sees between the input and 
source follower output, charging its 6.8nF feedback capacitor. Recovery 
occurs over milliseconds. The seriousness of these overdrive recovery 
problems is mitigated by the fact that with careful design it can take ap- 
proximately ±2V to saturate the MOSFET and ±5V to activate the pro- 
tection diodes. Thus, to overdrive the system, it takes a signal about ten 
times the full-scale input range of the pre-amp. 

I apologize for turning a simple, elegant, single transistor source fol- 
lower into the "bootstrapped, two-path impedance converter." But as I 
stated at the beginning, it is the combination of requirements that drives 
us to such extremes. It is very hard to meet all the requirements at once 
with a sintple circuit. In the next section, I will extend the two-path tech- 
nique to the attenuator to great advantage. Perhaps there the two-path 
method will fully justify its complexity. 

Th# Attenuator 

I have expended a large number of words and pictures on the impedance 
converter, so I will more briefly describe the attenuator. I will confine 
myself to an introduction to the design and performance issues and then 
illustrate some interesting altematives for constructing attenuators. The 
purpose of the attenuator is to reduce the dynamic range requirements 
placed on the impedance converter and pre-amp. The attenuator must 
handle stresses as high as +400V, as well as electrostatic discharge. The 
attenuator maintains a IMtl input resistance on all ranges and attains 
microwave bandwidths with excellent flatness. No small-signal micro- 
wave semiconductors can survive the high input voltages, so high- 
frequency oscilloscope attenuators are built with all passive components 
and electromechanical relays for switches. 

Figure 7-15 is a simplified schematic of a IMQ attenuator. It uses two 
stages of the well-known "compensated voltage divider" circuit One 
stage divides by five and the other by 25, so that division ratios of 1, 5, 
25, and 125 are possible. There are two key requirements for the attenua- 
tor. First, as shown in Figure 7-3, we must maintain RjCi = R2C2 in the 
-r5 stage to achieve a flat frequency response. A similar requirement 
holds for the ^-25 stage. Second, the input resistance and capacitance at 
each stage must match those of the impedance converter and remain very 



Signal Conditioning in Oscilloscopes and the Spirit of Invention 



Figure 7-1 5. 

A simplified 
two-stage high- 
impedance 
attenuator. 



nearly constant, independent of the switch positions. This requirement 
assures that we maintain attenuation accuracy and flatness for all four 
combinations of attenuator relay settings. 

Dividing by a high ratio such as 125 is similar to trying to build a high- 
isolation switch; the signal attempts to bypass the divider, caiising feed- 
through problems. If we set a standard for feedthrough of less than one 
least-significant bit in an 8-bit digital oscilloscope, the attenuator must 
isolate the input from the output by 201ogio(125 •28) = 90dB! I once spent 
two months tracking down such an isolation problem and traced it to 
wave guide propagation and cavity resonance at 2GHz inside the metallic 
attenuator cover. 

Relays are used for the switches because they have low contact im- 
pedance, high isolation, and high withstanding voltages. However, in a 
realm where 1mm of wire looks like a transmission line, the relays have 
dreadful parasitics. To make matters worse, the relays are large enough 
to spread the attenuator out over an area of about 2 x 3cm, Assuming a 
propagation velocity of half the speed of light, three centimeters takes 
200ps, which is dangerously close to the 700ps rise time of a 500MHz 
oscilloscope. In spite of the fact that I have said we can have no trans- 
mission lines in a high-impedance attenuator, we have to deal with them 
anyway! To deal with transmission line and parasitic reactanee efFects, a 
real attenuator includes many termination and damping msistors not 
shown in Figure 7-15. 

Rather than going into extreme detail about the conventional attenuator 
of Figure 7-15, it would be more interesting to ask if we could somehow 
eliminate the large and unreliable electromechanical relays. Consider the 
slighdy different implementation of the two-path impedance converter 
depicted in Figure 7-16. The gate of the depletion MOSFET is self-bi- 
ased by the 22MQ, resistor so that it operates at zero gate source voltage. 
If the input and output voltages differ, feedback via the op amp and bipo- 
lar current source reduces the error to zero. To understand this circuit, it 
helps to note that the impedance looking into the source of a self -biased 
FET is very high. Thus the collector of the bipolar current source se^ a 




-1-25 relay control 



/ 

R3 




"A 


C3 ~ 


C4 ^ 


o 

> R4 



^25 



Impedance 
Converter 

Output 
XI > > 




78 



Steve Roach 



Vin > 



Bootstrapped 
Depletion MOSFET 




out 



FigMfe7-16. 

A variation on the 
two-path imped- 
ance Gonverter. 



high-inipedance load. Slight changes in the op amp output can therefore 
produce significant changes in the circuit output. 

The impedance converter of Figure 7-16 can easily be turned into 
a figced attenuator, as shown in Figure 7-17. As before, there is a high- 
frequency and a low-frequency path, but now each divides by ten. There 
is an analog multiplier in the feedback path to make fine adjustments 
to the low-frequency gain. The multiplier matches the low- and high- 
frequency paths to achieve a high degree of flatness. A calibration pro- 
cedure determines the appropriate gain for the multiplier. 

Now we can build a complete two-path attenuator with switched atten- 
uation, as shown in Figure 7-18 (Roach 1992). Instead of cascading at- 
tenuator stages, we have arranged them in parallel. In place of the two 
double-pole double-throw (DPDT) relays of Figure 7-15, we now need 
only two single-pole single-throw (SPST) relays. Note that there is no 
need for a switch in the ^100 path because any signal within range for 



Vin> 



1MQ 



Bootstrapped 
Depi^ion MOSFET 




'out 



Low frequency 
Gain Control 



Figure 7-17. 

An attenuating 
impedance 
converter, or 
Iwo-path 
attenuator." 



1CX)Kfl 
-AAAr 



79 



Signal Conditioning in Oscilloscopes and the Spirit of Invention 



Figure 7-18. 

A two-path attenua- 
tor and impedance 
converter using 
only two SPST 
electromechanical 
relays. The protec- 
tion diodes and 
some resistors are 
omitted for clarity. 



^1 



-MO 



-r1CX) 



20pF 



(relay) ' 



IpF 
(relay) ' ' 



L-VW-. 

9pF^ ^ 

\7 



0.1 pF 



9.9pF 



1MQ 




Analog 
Multiplexor 



Attenuation 
Select 

Low Frequency ^ 
Gain Control 



-0 



1MQ 
-AAAr- 



100KQ 
-AAAr- 



10KQ 
-AAAr- 



Semiconductor 
Switches 



MO 



MOO 



the or -rlO path is automatically in range for the -r 100 path. The 
switches in the low-frequency feedback path are not exposed to high 
voltages and therefore can be semiconductor devices. 

A number of advantages accrue from the two-path attenuator of Figure 
7-18. The SPST relays are simpler than the original relays, and the high- 
frequency path is entirely AC coupled! The relays could be replaced with 
capacitive switches, eliminating the reliability problems of DC contects. 
One of the most important contributions is that we no longer have to pre- 
cisely trim passive components as we did in Figure 7-15 to make R^Cj = 
R2C2. This feature eliminates adjustable capacitors in printed circuit (PC) 
board attenuators and difficult laser trimming procedures on hylmds. With 
the need for laser trimming eliminated, we can build on inexpensive PC 
board attenuators that formerly required expensive hybrids. 



80 



Steve Roach 



Figure 7-19. 

Using the 
protection diodes 
as switehes in the 

^10 path. 

-^To Multiptexor 

Low Frequency 
Feedback 



We can take the new attenuator configuration of Figure 7-18 further. 
First observe that we can eliminate the 4-10 relay in Figure 7~18, as 
showii in FigiHre 7-19. The diodes are reverse biased to turn the ^10 path 
on and forward biased to turn it off. Forward biasing the diodes shorts the 
ipF capacitor to ground, thereby shunting the signal and cutting off the 
■f 10 path. The input capacitance changes by only O.lpF when we switch 
the -f 10 path. 

Now we are down to one electromechanical relay in the -J-1 path. We 
can eliminate it by moving the switch from the gate side of the source 
follower EdET lotl^ tein and source, as shown in Figure 7-20. In doing 
so we have made two switches from one, but that will turn out to be a 
good trade. With the ^1 switches closed, the drain and source of the FET 
are connected to the circuit and the -f 1 path functions in the usual man- 
ner. The protection diodes are biased to ±5 V to protect the FET 

To cut off the -^-1 path, the drain and source switches are opened, leav- 
ing those terminals floating. With the switches open, a voltage change at 



CMOS 
Logic Gates 




Vin >" 



+5V 
(-1) 

20pF 



r 



+50V 
(-M 0.100) 



22MQ 

-5V o— o V- o -50V 
(-^-10,100) 



^1 : Closed 
'^10,100: Open 



To Multiplexor 



Figure 7-20. 

Moving the -rl 
switch from the 
high4mpedance 
input side to the 
low-impedance 
output side of 
the FET 



Low Frequency 
Feedback 



81 



Signal Conditioning in Oscilloscopes and the Spirit of Invention 



Flpre7-21. 

Using PIN diodes 
to eliminate the 
relays in the 
■r1 path. 



the input drives the gate, source, and drain of the FET through an equal 
change via the 20pF input capacitor and the gate-drain and gate-source 
capacitances. Since all three terminals of the FET remain at the same 
voltage, the FET is safe from overvoltage stress. Of course, the switches 
must have very low capacitance in the open state, or capacitive voltage 
division would allow the terminals of the FET to see differing voltages. 
In -rlOO mode, the floating FET will see 40V excursions (eight divisions 
on the oscilloscope screen at 5V per division) as a matter of course. For 
this reason the -rl protection diodes must be switched to a higher bias 
voltage (±50V) when in the -^10 and ^100 modes. The switches that con- 
trol the voltage on the protection diodes are not involved in the high- 
frequency performance of the front-end and therefore can be 
implemented with slow, high-voltage semiconductors. 

Can we replace the switches in the drain and source with semiconduc- 
tor devices? The answer is yes, as Figure 7-21 shows. The relays in the 
drain and source have been replaced by PIN diodes. PIN diodes are made 
with a p-type silicon layer (P), an intrinsic or undoped layer (I), and an 
n-type layer (N). The intrinsic layer is relatively thick, giving the diode 
high breakdown voltage and extremely low reverse-biased capacitance. 
A representative packaged PIN diode has lOOV reverse breakdown and 
only O.OSpF junction capacitance. To turn the -rl path of Figure 7-21 on, 
the switches are all set to their ' ~1" positions. The PIN diodes are then 
forward biased, the bipolar transistor is connected to the op ani^, and the 
FET is conducting. To turn the path off, the switches are set to their 
"-f-10,100" positions, reverse-biasing the PIN diodes. Since these switches 



+15V 

(-1)' 



-50V 
(^10,100) 



Vin >- 



+5V > 
(-1) 

20 pF 



+50V 
(^10,100) 



is: 



+5V 
(-1) 



V -50V 

(-r10,100) 



22MQ 



P-i-N 
Diode 



P-I-N 
Diode 



->To Multiplexor 



^ Low Frequency Feedback 
from Op Amp 



-15V. 

(-1) 



\ +50V 
(^10.100) 



82 



are not involved in the high-frequency signal path, they too can be built 
with slow, high-voltage semiconductors. 

The complete circuit is now too involved to show in one piece on the 
page of a book, so please use your imagination. We have eliminated all 
electromechanicai switches and have a solid-state oscilloscope front- 
end. Although I had a great deal of fun inventing this circuit, I do not 
think it points the direction to future oscilloscope front-ends. Already 
research is under way on microscopic relays built with semiconductor 
micro-machining techniques (Hackett 1991). These relays are built on 
the surface of silicon or gallium arsenide wafers, using photolithography 
techniques, and measure only 0,5mm in their largest dimension. The 
contacts open only a few microns, but they maintain high breakdown 
voltages (100s of volts) because the breakdown voltages of neutral gases 
are highly nonlinear and not even monotonic for extremely small spac- 
ing. The contacts are so small that the inter-contact capacitance in the 
open state is only a few femtofarads (a femtofarad is 0.001 picofarads). 
Thus the isolation of the relays is extraordinary! Perhaps best of all, they 
are electrostatically actuated and consume near zero power. I believe 
micro-machined relays are a revolution in the wings for oscilloscope 
front-ends: I eagerly anticipate that they will dramatically improve the 
performance of analog switches in many applications. Apparently, even 
a device as old as the electromechanical relay is still fertile ground for 
a few ambitious inventors! 

References 



AdcHs, J, "Versatile Broadband Analog IC." VLSI Systems Design (September 1980): 

18-31. 

Andrews, J., A. Bell, N. Nahman, et. al. "Reference Waveform Flat Pulse Generator." 
IEEE Trans. InsL Meas, IM-32 (1) (March 1983): 27-32. 

Bama, A. "On the Transient Response of Emitter Followers." IEEE J. Solid State Circuits 
(June 1973): 233-235. 

Blinchikoff, H. and A. Zverev. Filtering in the Time and Frequency Domains. (New York: 
John Wiley & Sons, 1976). 

Evei, E. "DC Stabilized Wideband Amplifier." (Apr. 6, 1971): U.S. Patent #3,573,644. 

Hackett, R., L. Larsen, and M. Mendes. 'The Integration of Micro-Machine Fabrication 
with Electronic Device Fabrication on III-IY Semiconductor Materials." IEEE 
Trans. Comp. Hybrids, and Mfr. Tech. IEEE Trans. Comp. Hybrids, ondMfr. Tech 
(May 1991): 51-54. 

Kamath, B., G. Meyer, and P. Gray. "Relationship Between Frequency Response and 
Settling Time in (^rational Amplifiers." IEEE J. Solid State Circuits SC-9 (6) 
(December 1974): 347-352. 

Kimura, R. "DC Bootstrapped Unity Gain Buffer." (Apr, 30, 1991): U.S. Patent 

#5,012,134. 

Kozikowski, J. "Analysis and Design of Emitter Followers at High Frequencies." IEEE 
Trans, Circuit Theory (March 1964): 129-136. 

Roach, S. "Precision Programmable Attenuator." (Jun. 9, 1992): U.S. Patent #5,121,075. 



Signal Conditioning in Oscilloscopes and the Spirit of Invention 



Rush, K., W. Escovitz, and A. Berger. "High-Performance Probe System for a 1-GHz 
Digitizing Oscilloscope." Hewlett-Packard J. 37(4) (April 1986): 11-19. 

Rush, K., S. Draving, and J. Kerley. "Characterizing High Speed Oscilloscopes,*' fBEB 

Spectrum (Sep, 1990), 

Tektronix, Inc. Instruction Manual for the P6201 Probe. (Beaverton, Oregon. Tekironix, 
Inc., 1972). 



84 



William H. Gross 

8. OneTripl^nthelC 
DevetopmerTt Road 



This is the story of the last IC that I developed. I use the word develop 
rather than design because there is so much more involved in the making 
of a standard part than just the circuit design and layout. My goal is to 
give the reader an idea of what is involved in this total development. The 
majority of this description will be on the evolution of the product defini- 
tion and the circuit desi^ ^nce that is my major responsibility. I will 
also describe many of the other important steps that are part of the IC 
development. To give the reader an idea of what is required, I made an 
approximate list of the steps involved in the development of an IC. 
The steps in the development of a new IC: 

1. Definition 

2. Circuit design 

3. Re-definition 

4. More circuit design 

5 . The first finalizing of the specifications 

6. Test system definition 

7. Mask design 

8. Test system design 

9. Waiting for wafers to be made 

10. Evaluation 

11. Test system debug 

12. Redesign (circuit & masks) 

13. More waiting 

14. Finalizing the test system 

15. IC characterization 

16. Setting tile real specifications 

17. Pricing 

18. Writing the data sheet 

19. Promotion 

20. Yield enhancements 

Circuit design (steps 2, 4, and 1 2) is what we usually think of when 
we talk about IC design. As you can see, it is only a small part of the IC 
development. At some companies, particularly those that do custom ICs, 
circuit design is all the design engineers do. In the ideal world of some 
MBAs, the customer does the definition, the designer makes the IC, the 



85 



One Trip Down the IC Development Road 



test engineer tests, the market sets the price, and life is a breeze. This 
simple approach rarely develops an IC that is really new; and the coir^a- 
nies that work this way rarely make any money selling ICs. 

Most successful IC designers I know are very good circuit designers 
and enjoy circuit design more than anything else at work. But it is not 
just their circuit design skills that make these designers successful; it is 
also their realization that all the steps in the development of an IC must 
be done properly. These designers do not work to a rigid set of specifica- 
tions. They learn and understand what the IC specs mean to the customer 
and how the IC specs affect the system performance. Successfiil IC de- 
signers take the time to do whatever it takes to make the best IC they can. 

This is quite different from the custom IC designer who sells design. 
If you are selling design, it is a disadvantage to beat the customer's spec 
by too much. If you do the job too well, the customer willnot need a 
new custom IC very soon. But if you just meet the requirement, then in 
only a year or so the customer will be back for more. This kind of design 
reminds me of the famous Russian weight lifter who set many world 
records. For many years he was able to break his own world recOTd by 
lifting only a fraction of a kilogram more than the last time. He received 
a bonus every time he set a new world record; his job was setting rec- 
ords. He would be out of a job if he did the best he could every time; so 
he only did as much as was required. 

Product Definition 

Where do we get the ideas for new products? From our customers, of 
course. It is not easy, however. Most customers will tell you what they 
want, because they are not sure what they need. Also, they do not know 
what the different IC technologies are capable of and what trade-offs 
must be made to improve various areas of performance. The way ques- 
tions are asked often determines the answers. Never say, "Would you like 
feature XYZ?" Instead say, "What would feature XYZ be worth to you?" 

When an IC manufacturer asks a customer, it is often like a grandpar- 
ent asking a grandchild. The child wants all the things that it cannot get 
from its parents and knows none of the restrictions that bind the others. 
The only thing worse would be to have a total stranger do the question- 
ing. That may sound unlikely, but there are companies that have hired 
non-technical people to ask customers what new products they want. At 
best, this only results in a very humorous presentation that wastes a lot 
of people*s time. 

Talking to customers, applications engineers, and salespeople gives 
the clues and ideas to a designer for what products will be successful. It 
is important to pick a product based on the market it will serve. Do not 
make a new IC because the circuit design is fun or easy. Remember that 
circuit design is only a small part of the development process. The days 
of designing a new function that has no specific market should be long 



86 



William H. Gross 



gone. Although I have seen some products recently that appear to be 
solutions looking for problems! 

This is not to say that you need marketing surveys with lots of paper- 
work and calculations on a spreadsheet. These things are often man- 
agement methods to define responsibility and place blame. It is my 
experience that the errors in these forms are always in the estimate of the 
selling price and the size of the market. These inputs usually come from 
marketing and maybe that is why there is such a high turnover of person- 
nel in semiconductor marketing departments. After all, if the marketers 
who made the estimates change jobs every three years, no one will ever 
catch up with them. This is because it typically takes two years for devel- 
opment and two more years to see if the product meets its sales goals. 

So with almost no official marketing input, but based on conversations 
with many people over several years, I began the definition of a new 
product. I felt there was a market for an IC video fader and that the mar- 
ket was going to grow significantly over the next five years. The driving 
force behind this growth would be PC based multi-media systems. At the 
same time I recognized that a fader with only one input driven is a very 
good adjustable gain amplifier and that is a very versatile analog building 
block. The main source of this market information was conversations 
with customers trying to use a transconduetance amplifier that I had de- 
signed several years earlier in fader and gain control applications, 

Tl^Viieo Fader 

The first step is figuring out what a video fader is. The basic fader circuit 
has two signal inputs, a control input and one output. A block diagram of 
a fader is shown in Figure 8-1. The control signal varies the gain of the 
two inputs such that at one extreme the output is all one input and at the 
other extreme it is the other input. The control is linear; i.e., for the con- 
trol signal at 50%, the output is the sum of one half of input 1 and one 
half of input 2. If both inputs are the same, the output is independent of 
the control signal. Of course implementing the controlled potentiometer 
is the challenging part of the circuit design. 

The circuit must have flat response (O.ldB) from DC to 5MHz and low 
differential gain and phase (0.1% & O.l degree) for composite video 
applications. For computer RGB applications the -3dB bandwidth must 
be at least 30MHz and the gain accuracy between parts should be better 
than 3%. The IC should operate on supply voltages from +5V to ±15V, 
since there are still a lot of systems today on ±12V even though the trend 
is to ±5V. Of course if the circuit could operate on a single +5V supply, 
that would be ideal for the PC based multi-media market. 

The control input can be in many forms. Zero to one or ten volts is 
common as are bipolar signals around zero. Some systems use current 
inputs or resistors into the sununing node of an op amp. In variable gain 
amplifier applications often several control inputs are summed together. 



87 



One Trip Down the IC Development Road 



Figure 8-1. 

Basic fader circuit. 



CONTROL 




OUT 



In order to make a standard IC that is compatible with as many systems 
as possible, it is desirable to make the control input user defined. At the 
same time it is important that the IC not require a lot of external parts. 

To make the circuit more immune to errors in the potentiometer cir- 
cuit, we can take feedback from the output back to both inputs* Figure 
8-2 shows this feedback and replaces the potentiometer with the mathe- 
matical equivalent blocks: K, 1-K, and summation. Now the output is 
better controlled, since the value of K does not determine the total gain, 
only the ratio of the two input signals at the output. The gain is set by 
the feedback resistors and, to a smaller degree, the openloop gain of the 
amplifiers. 




88 



Wiiliam H. Gross 



Circuils 

At this point it is time to look at some actual circuits. Do we use voltage 
feedback or current feedback? Since the current feedback topology has 
inherently better linearity and transient response, it seemed a natural for 
the input stages. One customer showed me a class A, current feedback 
circuit being implemented with discrete transistors. Figure 8-3 shows the 
basic circuit. For the moment we will not concern ourselves with how the 
control signal, V^, is generated to drive the current steering pairs. Notice 
that the fader is operating inverting; for AC signals this is not usually a 
problem, but video signals are uni-polar and another inversion would 
eventually be needed. I assumed that the inverting topology was chosen 
to reduce the amount of distortion generated by the bias resistors, R^^ 
and Rb2» ^he input stages. 

Since transistors are smaller than resistors in an IC, I intended to re- 
place the bias resistors with current sources. Therefore my circuit could 
operate non-inverting as well as inverting, and as a bonus the circuit 
would have good supply rejection. The complementary bipolar process 
that I planned to use would make class AB implementations fairly 
straightforward. I began my circuit simulations with the circuit of Figure 
8-4; notice that there are twice as many components compared to the 
discrete circuit and it is operating non-inverting. 

After a bit of tweaking the feedback resistor values and the compen- 
sation capacitor, the circuit worked quite well. The transistor sizes and 




89 



One Trip Down the IC Development Road 



Figure 8-4. 
Class AB current 
feedback fader. 




V"- V" 



current levels were set based on previous current feedback amplifiers 
already designed. It was time to proceed to the control section. 

For linear control of the currents being steered by a differential pair, 
the voltage at the bases of the steering transistors must have a nonlinear 
characteristic. This TANH characteristic is easily generated with "pre- 
distortion" diodes. The only requirement is that the currents feeding the 
diodes must be in the same ratio as the currents to be steered. The circuit 
of Figure 8-5 takes two input control currents, K and ( UK), and uses Ql 
and Q2 as the pre-distortion diodes to generate the control signal V^j^ for 
the NPN steering transistors. The collector currents of Ql and Q2 then 
feed the pre-distortion diodes Q3 and Q4 that generate V^,p to control the 
PNP steering transistors. 

I noticed that the linearity of the signal gain versus diode current is 
strongly influenced by the bulk and of the current steering tran- 
sistors. After consulting some papers on multipliers (thank you Barry 
Gilbert) I found that there are some topologies where the bulk R^^ and R^ 
of the pre-distortion diodes compensate the equivalent in the steering 



90 



William H. Gross 



BIAS- 



Qk Q(1-K) 




¥ TO MIRROR Figure 8-5. 

Basic circuit to 
drive the steering 
transistors. 



TO MIRROR 



transistors. Unfortunately, in my circuit I am using PNPs to drive NPNs 
and vice versa. In order to match the pre-distortion diodes to the steering 
transistors, a more complicated circuit was required. I spent a little time 
and added a lot more transistors to come up with a circuit where the 
pre-distortion diodes for the NPN steering transistors were NPNs, and 
the same for the PNPs. Imagine my surprise when it didn't solve the lin- 
earity problem. I have not included this circuit because I don't remember 
it; after all, it didn't work. 

So I had to leara a little more about how my circuit really worked. In 
the fader circuit, the DC current ratio in the steering transistors is not im- 
portant; the small signal current steering sets the ratio of the two inputs. 
Figure 8-6 shdws a simplified circuit of the pre-distortion diodes and the 
steering transistors. The diodes and transistors are assumed perfect with 
18ii i^sistors in series with the emitters to represent the bulk R^^ and of 
the devices. The control currents are at a 10:1 ratio; the DC currents in the 



1.0mA, DC 
9.5pA, AC 



O.lmA, DC 
1.5uA, AC 




Vbe = eoomv 

18Q 



VBE = 600mV VBE = 660mV 



10:1 RATIO INPUT DC 
10:1 RATIO OUTPUT DC 
6.33:1 RATIO OUTPUT AC 



Figure 8-^. 
Bulk resistance 
problems in 
steering. 



91 



OnelYtp Down the IC Development Road 

steering transistors are also at a 10:1 ratio. But the small signal steering is 
set by the ratio of the sum of the r^ and the bulk resistance in each transis- 
tor, and in this case the result is a 6.33:1 ratio! 

In the fader circuit, the only way to improve the gain accuracy is with 
low and steering transistors. Unfortunately this requires larger tran> 
sistors running at low current densities and that significantly reduces the 
speed (F-tau) of the current steering devices. I went back to the simpler 
circuit of Figure 8-5, increased the size of the current steering transis- 
tors, and tweaked the compensation capacitor and feedback resistors to 
optimize the response. 

Now it was time to find a way to interface the external control sig- 
nals) to the pre-distortion diodes of Figure 8-5. The incoming signal 
would have to be converted to a current to drive the pre-distortion diodes, 
Ql and Q3. A replica of that current would have to be subtracted from 
a fixed DC current and the result would drive the other pre-distortion 
diodes, Q2 and Q4. 

I did not want to include an absolute reference in this product for sev- 
eral reasons. An internal reference would have to be available for the ex- 
ternal control circuitry to use, in order not to increase the errors caused by 
multiple references. Therefore it would have to be capable of significant 
output drive and tolerant of unusual loading. In short, the internal refer-^ 
ence would have to be as good as a standard reference. The inaccuracy of 
an intemal reference would add to the part-to-part variations unless it was 
trimmed to a very accurate value. Both of these requirements would in- 
crease the die size and/or the pm count of the IC. Lastly, there is no stan- 
dard for the incoming signals, so what value should the referenee be? 

I decided to require that an external reference, or "full scale" voltage, 
would be applied to the part. With an external full scale and control volt- 
age, I could use identical circuits to convert the two voltages into two 
currents. The value of the full scale voltage is not critical because only 
the ratio between it and the control voltage matters. With the same circuit 
being used for both converters, the ratio matching should be excellent. 

Figure 8-7 shows the basic block diagram that I generated ti> deter- 
mine what currents would be needed in the control section. The gain 
control accuracy requirements dictated that an open loop voltage-tb- 
current converter would be unacceptable. Therefore a simple op amp 
with feedback would be necessary. It became clear that two control cur- 
rents (I^) were needed but only one full scale current (Ipg) was. Mirror #1 
must have an accurate gain of unity in order to generate the proper differ- 
ence signal for mirror #3. Mirrors 2 and 3 must match well, but their 
absolute accuracy is not important. AH three mirrors must operate from 
zero to full scale current and therefore cannot have resistive degeneration 
that could change their gain with current level. 

In order to use identical circuits for both voltage-to-current converters, 
I decided to generate two full scale currents and use the extra one to bias 
the rest of the amplifiers. You can never have too many bias currents 
available. 



92 



William H. Gross 



MIRROR 




MIRROR 


#2 




#3 




BIAS 



Figure 8-7. 

Block diagram of 
the control circuit. 



The block diagram of Figure 8-7 became the circuit of Figure 8-8 
after several iterations. The common mode range of the simple op amp 
includes the negative supply and the circuit has sufficient gain for the job. 
Small current sharing resistors, Rl, R2, R3, and R4, were added to im- 
prove the high current matching of the two output currents and eliminate 
the need for the two R^ resistors. The small resistors were scaled so they 
could be used for short circuit protection with Q5 and Q6 as well. 

MifTor #1 is a "super diode" connection that reduces base current errors 
by beta; the diode matches the collector emitter voltages of the matched 
transistors. Identical mirrors were used for #2 and #3 so that any errors 
would ratio out. Since these mirrors feed the emitters of the pre-distortion 
cascodes Ql and Q2, their output impedance is not critical and they are 
not cascoded. This allows the bias voltage at the base of Ql and Q2 to be 
only two diode drops below the supply, maximizing the common mode 
range of the input stages. 

While evaluating the full circuit, I noticed that when one input was 
supposed to be off, its input signal would leak through to the output. The 
level inareased with frequency, as though it was due to capacitive feed- 
through. The beauty of SPICE came in handy now. I replaced the current 
steering transistors with ideal devices and still had the problem. Slowly 
I came to the realization that the feedthrough at the output was coming 
from the fi^b^k resistor. In a current feedback amplifier, the inverting 
input is driven from the non-inverting input by a buffer amp and therefore 
the input signal is always present at the inverting input. Therefore the 
amount of signal at the output is just the ratio of the feedback resistor to 
the amplifier output impedance. Of course the output impedance rises 
with frequency because of the single pole compensation necessary to keep 



93 



One Trip Down the IC Development Road 



Figure 8-8. 

The control circuit. 




MIRROR MIRROR MIRROR 

#1 #2 #3 

^ IJ U 

11 rii fii 



01 




TO BIAS THE AMPLIFIERS 



Q2 



eiAs 



the amplifier stable. The basic current feedback topology I had chosen was 
the feedthrough problem. Now it was obvious why the discrete circuit was 
operating inverting. The problem goes away when the non-inverting input 
is grounded because then the inverting input has very little signal on it- 



Redefinition 



At this point I realized I must go back to the beginning and look at volt- 
age feedback. I started with the basic folded cascode topology and 
sketched out the circuit of Figure 8-9. It seemed to work mid th^ were 
no feedthrough problems. It also appeared to simplify the control re- 
quirements, since there were no PNPs to steer. While working with this 
circuit I realized that the folded cascode transistors, Q7 and Q8, could be 
used as the steering devices, and sketched out Figure 8-- 10. This looked 
great since it had fewer devices in the signal path and therefore better 
bandwidth. The only downside I could see was the critical matching of 
the current sources; all eight current sources are involved in setting the 
gain. While I was pondering how to get eight current sources coming 



94 



WjiHamH. Gross 




+ 1 >— f OUT 



from opposite supplies to match, I decided to run a transient response to 
determine how much input degeneration was required. 

The bottom fell out! When the fader is set for 10% output, the differ- 
ential input voltage is 90% of the input signal! This means that the open 
/oflp linearity of the input stage must be very good for signals up to one 
volt or more. To get signal linearity of 0.1% would require over a volt of 
degeneration. With that much degeneration in each input stage, the mis- 
match in offset voltage between the two would be tens of millivolts and 
that would show up as control feedthrough. Big degeneration resistors 



fader. 




One Trip Down the IC Development Road 



also generate serious noise problems and cause the tail pole to move in, 
reducing the speed of the amplifier. It was time to retreat to the current 
feedback approach and see how good I could make it. 

The current feedback topology has very low feedthrougb when oper- 
ated inverting, so I started with that approach. Unfortunately the feed- 
through was not as good as l expected and I started looking for the cause. 
The source of feedthrough was found to be the emitter-base capacitance 
of the current steering transistor coupling signal into the pre-distortion 
diode that was holding the transistor off. Unfortunately the off diode was 
high impedance (no current in it) so the signal then coupled thix>ugh the 
collector base capacitance of the steering transistor into the collector, 
where it was not supposed to be. Since the steering transistors had to be 
large for low and R^, the only way to eliminate this problem was to 
lower the impedance at the bases of the steering transistors. 

What I needed was four buffer amplifiers between each of the four 
pre-distortion diodes and the current steering transistors. To preserve the 
pre-distortion diodes' accuracy, the input bias current of the buffers 
needed to be less than one microamp. The offset of the buffers had to 
be less than a diode drop in order to preserve the input stage common 
mode range so that the circuit would work on a single 5V supply. Lastly, 
the output impedance should be as low as possible to minimize the 
feedthrough. 

The first buffer I tried was a cascode of two emitter followers » as 
shown on the left in Figure 8-1 1 . By varying the currents in tte followers 
and looking at the overall circuit feedthrough, I determined that the out- 
put impedance of the buffers needed to be less than 75Q, for an accept- 
able feedthrough performance of 60dB at 5MHz. I then tried several 
closed loop buffers to see if I could lower the supply current. The circuit 
shown in Figure 8-1 1 did the job and saved about 200 microamps of 
supply current per buffer. The closed loop buffer has an output imped- 
ance of about 7n that rises to 65£2 at 5MHz. Since four buffers were 
required, the supply current reduction of 800 microamps was significant. 

At this point it became obvious to me that for the feedthrough to be 
down 60dB or more, the control circuitry had to be very accurate. If the 
full scale voltage was 2.5V and the control voltage was OV, the offset 
errors had to be less than 2.5mV for 60dB of off isolation. Even if I 
trimmed the IC to zero offset, the system accuracy requirement was still 
very tough. I therefore wanted to come up with a circuit that would in- 
sure that the correct input was on and the other input was fully off when 
the control was close to zero or full scale. I thought about adding inten- 
tional offset voltage and/or gain errors to the V-to-I converters to get this 
result, but it didn't feel good. What was needed was an internal circuit 
that would sense when the control was below 5% or above 95% and force 
the pre-distortion diodes to 0% and 100%. Since the diodes were fed 
with currents, it seemed that sensing current was the way to go. 

Since the currents that feed the pre-distortion diodes come from iden- 
tical mirrors, I wanted to see if I could modify the mirrors so that they 



96 



William Gross 




Figure 8-11 
Open- and closed- 
loop buffers. 



would turn off at low currents. This would work at both ends of the con- 
trol signal because one mirror is always headed towards zero current. The 
first thought was to put in a small fixed current that subtracted from the 
input current. This would add an offset near zero (good) and a gain error 
everywhere else (bad). Now if I could turn off the offset current when the 
output current was on, it would be perfect. Current mirrors #2 and #3 in 
Figure 8-8 were each modified to be as shown in Figure 8-12. The offset 
current is generated by Q9. A small ratio of the output current is used to 
turn off Q9 by raising its emitter. The ratios are set such that the output 
goes to zero with the input at about 5% of full scale. The nice thing about 
this mirror is that the turn-off circuit has no effect on mirror accuracy for 
inputs of 10% or more. The diode was added to equdize the collector- 
base voltage of all the matching transistors. 

At this point the circuit was working very well in the inverting mode 
and I went back to non-inverting to see how the feedthrough looked. 
Since the output impedance of the amplifier determines the feedthrough 
performance, I eliminated all the output stage degeneration resistors. I 
set the output quiescent current at 2.5 milliamps so the output devices 
would be well up on then- F-tau curve and the open loop output imped- 
ance would be well under 10 Ohms, The feedthrough was still 60dB 
down at 5MHz. I added a current limit circuit that sensed the output tran- 
sistors* collector current, and the circuit topology was finalized. 




Figure ft-12. 
Mirror with a 
turn-off. 



WG1? 



97 



One Trip Down the tC Development Road 



The last step in the circuit design is rechecking and/or optimi/ing the 
area of every transistor. This is usually done by checking the circuit's 
performance over temperature. I always add a little extra area to the tran- 
sistors that are running close to saturation when the additional parasitic 
capacitance won't hurt anything. 

Mask Design 

Experienced analog IC designers know how important IC layout is. Tran- 
sistors that are supposed to match must have the same emitter size and 
orientation as well as the same temperature. The fader output amplifier is 
capable of driving a cable and generating significant thermal gradients in 
the IC. For this reason I put both input stages on one end of the die next 
to the current steering devices and put the output stage at the other end. 
The bias circuits and the control op amps went in the middle. The best 
way to minimize thermal feedback is distance. The 14-pin SO package 
set the maximum die size and the pad locations. 

The IC process used had only one layer of metalization and therefore I 
provided the mask designer with an estimate of where "cross-unders" 
would be needed. For those of you not familiar with the term "cross- 
under," I will explain. A cross-under is a small resistor, usually made of 
N+, inserted in a lead so that it can "cross-under" another metal trace. 
Normally these cross-unders are inserted in the collectors of transistors, 
since a little extra resistance in the collector has minimal effect. 

The fader circuit, with over 140 transistors and very few resistGrs, was 
clearly going to have a lot of cross-unders. I was resigned that both sup- 
plies would have many cross-unders; in order for the circuit to work prop- 
erly, the voltage drops introduced by the cross-unders must not disturb the 
circuit. For example, the current mirrors will common mode out any vari- 
ation in supply voltage as long as all the emitters are at the saine voltage. 
This is easy to do if the emitters all connect together on one trace and 
then that trace connects to the supply. As mask design progresses, it is 
important that each cross-under added to the layout be added to the 
schematic and that circuit simulation is re-checked. Time spent before the 
silicon comes out to insure that the circuit works is well spent. 

I would like to make a comment or two on mask design and the time 
that it takes. For as long as I can remember, speeding up mask design has 
been the Holy Grail. Many, including myself, have thought that some new 
tool or technique will cut the time required to layout an IC significantly. 
When computer layout tools became available, they were sold as a pro- 
ductivity enhancement that would cut the time it taices to layout ICs. The 
reality was that the ICs became more complex and the time stayed about 
the same. 

The analog ASIC concept of a huge library of functions available as 
standard cells that are just plopped down and hooked up sounds great; 
except that very few innovative products can be done with standard func- 



98 



William H. Gro^s 



lions. What typically happens is that each new product requires modifica- 
tions to the "standard" cells or needs some new standard cells. You're 
right back at transistor level optimizing the IC. Of course no one ever 
plans for the extra time that this transistor level optimization takes, so the 
project gets behind schedule. 

The "mono-chip" or "master-chip" idea is often used to speed up de- 
velopment. This technique uses just the metal layer(s) to make the new 
product; a large standard IC with many transistors and resistors is the 
common base. The trade-off for time saved in mask design is a larger die 
size. Tlie argument is often made that if the product is successful, a fiill 
re-layout can be done to reduce die size and costs. Of course, this would 
then require all the effort that should have been done in the first place. I 
would not argue to save time and money up front because I did not ex- 
pect my part to be successful! 

In summary, mask design is a critical part of analog IC development 
and must be considered as important as any other step. Doing a poor job 
of mask design will hurt performance and that will impact the success of 
a product much more than the extra time in development, 

Tesliflg 

IC automatic test system development is an art that combines analog 
hardware and software programming. We cannot sell performance that 
we cannot test. It is much easier to measure IC performance on the bench 
than in an automatic handler. In successful companies, the good test de- 
velopment engineers are well respected. 

The fader IC requires that the closed loop AC gain be measured very 
accurately. The gain is trimmed at wafer sort by adjusting the value of 
resistor R^. This trim is done with the control input fixed and the linearity 
of the circuit determines the gain accuracy elsewhere. The errors due to 
the bulk resistance of the steering transistors have no effect at 50% gain; 
therefore it seemed like the best place to trim the gain. 

While characterizing the parts from the first wafer, I noticed that there 
were a few parts that had more error than I expected at 90% gain. I also 
determined that these parts would be fine if I had trimmed them at 90%. 
It was also true that the parts that were fine at 90% would not suffer from 
being trimmed at 90%. So, I changed my mind as to where the circuit 
was to be trimmed and the test engineer modified the sort program. More 
wafers were sorted and full characterization began. 

Setting the data sheet limits is a laborious process that seems like it 
should be simpler. The designer and product engineer go over the distri- 
bution plots from each test to determine the maximum and minimum 
limits. In a perfect world we would have the full process spread repre- 
sented in these distributions. Even with a "design of experiments" run that 
should give us the full spread of process variations, we will come up short 
of information. It's Murphy's law. This is where the designer's knowledge 



99 



One Trip Down the fC Development Road 



of which specs are important, and which are not, comes into play. It 
makes no sense to "over spec" a parameter that the customer is not eon- 
cemed about because later it could cause a yidd problem. On the other 
hand, it is important to spec all parameters so that any "sports" (oddball 
parts) are eliminated, since they are usually caused by defects and will 
often act strangely. The idea is to have all functional parts meet spec if 
they are normal. 

Data Sheets 

The data sheet is the most important sales tool the sales people have. 
Therefore it is important that the data sheet is clear and accurate. A good 
data sheet is always late. I say this based on empirical data, but there 
seems to be a logical explanation. The data sheet is useless unless it has 
all the minimums and maximums that guarantee IC performance; as soon 
as those numbers are known, the part is ready to sell and we iieed the 
data sheet. Of course it takes time to generate the artwork and print the 
data sheet and so it is late. One solution to this problem is to put out an 
early, but incomplete, data sheet and then follow it a few months later 
with a final, complete one. 

Analog ICs usually operate over a wide range of conditions and the 
typical curves in the data sheet are often used to estimate the IC perfor- 
mance under conditions different from those described in the eteetrical 
table. The generation of these curves is time consuming arid, when done 
well, requires a fair amount of thought. Human nature being what it is, 
most people would rather read a table than a graph, even though a table is 
just an abbreviated version of the data. As a result, the same information 
is often found in several places within the data sheet. I am often amazed 
at how inconsistent some data sheets are; just for fun, compare the data 
on the front page with the electrical tables and the graphs. 

Beware of typical specs that are much better than the minimums and 
maximums. I once worked with a design engineer who argued that the 
typical value should be the average of the distribution; he insisted that the 
typical offset voltage of his part was zero even though the limits were 
±4mV. Most companies have informal definitions of "typical", and it 
often varies from department to department. George Erdi added a note to 
several dual op amp data sheets defining the typical value as the value 
that would yield 60% based on the distributions of the individual ampli- 
fiers. I like and use this definition but obviously not everyone does, since 
I often see typicals that are 20 times better than the limits 1 Occasionally 
the limits are based on automatic testing restrictions and the typicals 
are real; for example, CMOS logic input leakage current is less than a 
few nanoamps, but the resolution of the test system sets the limit at 1 
microamp. 



100 



William H. Gross 



Summary 

Since you are still reading, I hope this long-winded trip was worth it. The 
development of an IC is fun and challenging. I spent most of this article 
describing the circuit design because I like circuit design. I hope, how- 
ever, that I have made it clear how important the other parts of the devel- 
opment process are. There are still more phases of development that I 
have not mentioned; pricing, press releases, advertimg, and applications 
support are all part of a successful new product development. At the time 
of this writing, the video fader had not yet reached these phases. Since I 
am not always accurate at describing the future, I will not even try. Those 
of you who want to know more about the fader should see the LT1251 
data sheet. 

At this time I would like to thank all of the people who made the video 
fader a reality and especially Julie Brown for mask design, Jim Sousae 
for characterization, Dung (Zoom) Nguyen for test development, and 
Judd Murkland in product engineering. It takes a team to make things 
happen and this is an excellent one. 



101 



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James M. Bryant 



9. Analog Breadboarding 



Introduction 

While there is no doubt that computer analysis is one of the most valu- 
able tools that the analog designer has acquired in the last decade or so, 
there is equally no doubt that analog circuit models are not perfect and 
must be verified with hardware. If the initial test circuit or "breadboard" 
is not correctly constructed it may suffer from malfunctions which are 
not the fault of the design but of the physical structure of the breadboard 
itself. This chapter considers the art of successful breadboarding of high- 
performance analog circuits. 

The successful breadboarding of an analog circuit which has been 
analyzed to death in its design phase has the reputation of being a black 
art which can only be acquired by the highly talented at the price of infi- 
nite study and the sacrifice of a virgin or two. Analog circuitry actually 
obeys the very simple laws we leamed in the nursery: Ohm's Law, 
Kirchoff 's Law, Lenz's Law and Faraday's Laws. The problem, however, 
lies in Murphy's Law. 

Murphy's Law is the subject of many engineering jokes, but in its sim- 
plest form, *Tf Anything Can Go Wrong — It Will!", it states the simple 
truth that physical laws do not cease to operate just because we have over- 
looked or ignored them. If we adopt a systematic approach to breadboard 



MURPHY'S LAW 

Whatever can go wrong, will go wrong. 

Buttered toast, dropped on a sandy floor, 
falls butter side down. 

The basic principle behind Murphy's Law is that 
all physical laws always apply - 
when ignored or overlooked they do not stop working. 



Figure 9-1. 



103 



Analog Breadboarding 

construction it is possible to consider likely causes of circuit malfunction 
without wasting very much time. 

In this chapter we shall consider some simple issues whieh are likely 
to affect the success of analog breadboards, namely resistance (including 
skin effect), capacitance, inductance (both self inductance and mutual 
inductance), noise, and the effects of careless current routing. We shall 
then discuss a breadboarding technique which allows us to minimize the 
problems we have discussed. 



Resistance 



As an applications engineer I shall be relieved when room-temperature 
superconductors are finally invented, as too many engineers suppose that 
they are already available, and that copper is one of them. The assump- 
tion that any two points connected by copper ^e at the same potential 
completely overlooks the fact that copper is resistive and its resistance is 
often large enough to affect analog and RF circuitry (although it is rarely 
important in digital circuits). 



CONDUCTORS ARE NOT SUFEflCONDUCTORS 



Consider 10 cm of 1 mm PC track 



Standard track thickness is 0.038 mm 
p for copper Is 1 .724 X 10^ Q cm @ 25''C 

/. PCB sheet resistance is 0.45 mQ/sq 
Resistance of the track Is 45 mn 
THIS IS ENOUGH TO MATTER! 



Figure 9-2. 

The diagram in Figure 9-2 shows the effect of copper resistance at DC 
and LF. At HF, matters are complicated by "skin effect." Inductive effects 
cause HF currents to flow only in the surface of conductors. The skin 
depth (defined as the depth at which the current density has dropped to 
1/e of its value at the surface) at a frequency f is 
1 

where |i is the permittivity of the conductor, and a is its conductivity in 
Ohm-meters. |X = 47cxl0-^ henry/meter except for magnetic materials, 
where |Li=4jir7CXlO-^ henry/meter is the relative permittivity). For the 



104 



James tt. Bryant 



purposes of resistance calculation in cases where the skin depth is less 
than one-fifth the conductor thickness, we can assume that all the HF 
current flows in a layer the thickness of the skin depth, and is unifonnly 
distributed. 



SKfN EFFECT 

At high frequencies inductive effects cause currents to flow 
only In the surface of conductors. 

HFCurrinttfkM 

In ttilfi siiifMi Ifl^/mi. 




CONDUCTOR 



Skin depth at frequency f in a conductor of resistivity p ohm-metre 
and permittivity |i henry/metre is 




In copper the skin depth is ^* ^J^\J^ cm and 

the skin resistance is 2.6X10 n/sq 

(Remember that current /nay flow in both sides of a PCB 
[this is discussed later] and that the skin resistance formula 
is only vatid if the skin d^h is less than the conductor thickness.) 



Skin effect has the effect of increasing the resistance of conductors at 
quite modest frequencies and must be considered when deciding if the 
resistance of wires or PC tracks will affect a circuit's performance. (It 
also affects the behavior of resistors at HF.) 




Good HF analog design must incorporate stray capacitance. Wherever 
two conductors are separated by a dielectric there is capacitance. The 
formulae for parallel wires, concentric spheres md cylinders, and other 
more exotic structures may be found in any textbook but the commonest 
structure, found on all PCBs, is the parallel plate capacitor. 



105 



Analog Breadbaarding 



CAPACITANCE 

Wherever two conductors are separated by a dietectric 
(including air or a vacuum) there is capacitance. 

For a parallel pJate capacitor C = •^°'='^^r^ pp 

where A is the plate area in sq.cm 
d Is the ptate separation in cm 
& Er is the dielectric constant 

Epoxy RGB matenaJ Is often 1 .5 mm thick and E^ =4.7 
Capacity is therefore approximately 2.8 pf/sqxm 



Figure 9-4. 

When stray capacitance appears as parasitic capacity to ground it can 
be mininiized by careful layout and routing, and incorporated into the 
design/Where stray capacity couples a signal where it is not wanted the 
effect may be minimized by design but often must be cured by the use of 
a Faraday shield. 

Figure &-5. 



FARADAY SHIELDS 



S7 



Capacitively coupled noise can be very effectively shielded 
by a grounded conductive shield, known as a Faraday Shield. 
But it must be grounded or it increases the problem. 

For this reason coil and quartz crystat cans should always be grounded. 



If inductance is to be minimized the lead and PC track length of capac- 
itors must be kept as small as possible. This does not mean just generally 
"short," but that the inductance in the actual circuit function must be min- 
imal. Figure 9^ shows both a common mistake (the leads of the capaci- 
tor CI are short, but the decoupling path for ICl is very long) and the 



106 



James M. Bryant 



CAPACITOR LEADS MUST BE SHORT 



Figure 9-6. 



+V 




1 1 
I I 



Although the leads of CI are short the HF decoupling path of IC 1 is far too long. 
The decoupling path of IC2 is ideal. 



correct way to decouple an IC (IC2 is decoupled by C2 with a very short 
decoupling path). 



Any length of conductor has inductance and it can matter In free space a 
!cm length of conductor has inductance of 7-lOnH (depending on diam- 
eter), which represents an impedance of 4-6^ at lOOMHz. This may be 
large enough to be troublesome, but badly routed conductors can cause 
worse problems as they form, in effect, single turn coils with quite sub- 
stantial inductance. 



Any conductor has some inductance 
A straight wire of length L and radius R (both mm & L»R) 



A strip of conductor of length width W and thickness H (mm) 

has inductance 



Inductors 



INDUCTANCE 



Rgure 9-7. 



has inductance Q.2L In — h.75 nH 





1 cm ofthinwifttDr PCtracfcis$om«»i4t«r« batoMeA7and lOnH 



Analog Breadboarding 



INDUCTANCE 



Figure 9-8. 





A loop of conductor indtjc^ance - 
two acyacertt loops have rmitual inciiiclance. 



If two such coils are close to each other we must consider their mutual 
inductance as well as their self-inductance. A change of current in one 
will induce an EMF in the other. Defining the problem, of course, at once 
suggests cures: reducing the area of the coils by more careful layout, and 
increasing their separation. Both will reduce mutual inductance, and re- 
ducing area reduces self inductance too. 

It is possible to reduce inductive coupling by means of shields. At LF 
shields of munmetal are necessary (and expensive, heavy and vulnerable 
to shock, which causes loss of permittivity) but at HF a continuous 
Faraday shield (mesh will not work so well here) blocks magnetic fields 
too, provided that the skin depth at the frequency of interest is much less 

Rgure 9-9. 



INDUCTANCE 




Inductance is reduced by reducing loop area - 
mutual inductance is reduced by reducing loop area 
and increasing separation. 

Since the magnetic fields around colJs are dipole fields they attenuate with the cube of the 
distance - so increasing separation is a very effective way of reducing mutual inductance. 



108 



James M. Bf^nt 
Figure 9-10. 



MAGNiTIC SH^I^^ 

At LF magnetic shielding requires Mu-M^ which is 
heavy , expensive and vofnerable to shock. 

At HF a conductor provides effective magnetic shielding 
provided the sl<in depth is less than the conductor thickness. 

PC foil is an effective magnetic shield above 10-20 MHz. 



than the thickness of the shield. In breadboards a piece of copper^clad 
board, soldered at right angles to the ground plane, can make an excellent 
HF magnetic shield, as well as being a Faraday shield. 

Magnetic fields are dipole fields, and therefore the field strength di- 
minishes with the cube of the distance. This means that quite modest 
separation increases attenuation a lot. In many cases physical distance is 
all that is necessary to reduce magnetic coupling to acceptable levels. 

Grotinds 

Kirchoff 's Law tells us that return currents in ground are as important 
as signal currents in signal leads. We find here another example of the 
"superconductor assumption"— too many engineers believe that all 
points marked with a ground symbol on the circuit diagram are at the 
same potential. In practice ground conductors have resistance and induc- 
tance — ^and potential differences. It is for this reason that such bread- 
boarding techniques as matrix board, prototype bo^aris (the ones where 
you poke component leads into holes where they are gripped by phos- 
phor-bronze contacts) and wire-wrap have such poor performance as 
analog prototyping systems. 

The best analog breadboard arrangement uses a "ground pl^e" — a 
layer of continuous conductor (usually copper-clad board). A ground 

Figtife*-11. 



KIRCHGf^FS LAW 
The net Current at dfiy point in a circuit is zero. 

OR 

What flows in flows out again. 

OR 

Current flows in circles. 

THEREFORE 

Aii signals are differential. 

AND 

Ground tmfj^dance matters. 



109 



Analog Breadboarding 



plane has minimal resistance and inductance, but its impedance may still 
be too great at high currents or high frequencies. Sometimes a break in a 
ground plane can configure currents so that they do not interfere with each 
other; sometimes physical separation of different subsystems is sufficient, 

FiQiire9-12. 



GROUND PLANE BREADBOARD 



The breadboard ground consists of a single layer 
of continuous metal, usually (unetched) copper-clad PCB material. 

In theory all points on the plane are at the same potential, 
but in practice it may be necessary to configure ground currents by 
means of breaks in the plane, or careful placement of sub-systems. 
Nevertheless ground plane is undoubtedly the most effective ground 
technique for analog breadboards. 



Figure 9-13. 



GROUND PLANE 




NOTE: OseiHos^QpOf In-mp power groimctmd 
grotrndfAm mwt tit common for bias currents. 
Soffie Common^mbde voltage does not matter. 




To s|)ectruni 
analyser 



To measure voltage drop In grounci plane it is necessary to use 

a device with high common-mode rejection and low noise. 
At DC and LF an instrumentation amplifier driving an oscilloscope 
will give sensitivity of up to 5 pV/cm - at HF and VHF a 
transmission line transformer and a spectrum analyser can 
provide even greater sensitivity. 



110 



James M. Bryant 



It is often easy to deduce where currents flow in a ground plane, but in 
complex systems it may be difficult. Breadboards are rarely that com- 
plex, but if necessary it is possible to measure differential voltages of as 
little as 5yiV on a ground plane. At DC and LF this is done by using an 
instrumentation amplifier with a gain of 1,000 to drive an oscilloscope 
working at 5 mV/cm. The sensitivity at the input terminals of the inamp 
is S jiiV/cm; there will be some noise present on the oscilloscope trace, 
but it is quite possible to measure ground voltages of the order of l|xV 
with such simple equipment. It is important to allow a path for the bias 
current of the inamp, but its common-mode rejection is so good that this 
bias path is not critical. 

The upper frequency of most inamps is 25-50kHz (the AD830 is an 
exception— it works up to 50 MHz at low gains, but not at xl,000). 
Above LF a better technique is to use a broadband transmission line 
traBsformer to remove common-mode signals. Such a transformer has 
little or no voltage gain, so the signal is best displayed on a spectrum 
analyzer, with (iV sensitivity, rather than on an oscilloscope, which only 
has sensitivity of 5mV or so. 



The final issue we must consider before discussing the actual techniques 
of breadboarding is decoupling. The power supplies of HF circuits must 
be short-circuited together and to ground at eil frequencies above DC. 
(DC short-circuits are undesirable for reasons which I shall not bother to 
discuss.) At low frequencies the impedance of supply lines is (or should 
be) low and so decoupling can be accomplished by relatively few elec- 
trolytic capacitors, which will not generally need to be very close to the 
parts of the circuit they are decoupling, and so may be shared among 
several parts of a system. (The exception to this is where a component 
draws a large LF current, when a local, dedicated, electrolytic capacitor 
should be used.) 

At HF we cannot ignore the impedance of supply leads (as we have 
already seen in Figure 9-6) and ICs must be individually decoupled 
with low indtietance capacitors having short leads and PC tracks. Even 
2-3 mm of extra lead/track length may make the difference between the 
success and failure of a circuit layout. 



DecOUPLING 

Supplies must be short-circuited to each ottier 
and to ground at a// frequencies. 
(But not at DC.) 



Figure 9-14. 



til 



Analog Breadboarcling 




Where the HF currents of a circuit are mostly internal (as is the case 
with many ADCs) it is sufficient that we short-circuit its supplies at HF 
so that it sees its supplies as stiff voltage sources at all frequencies. 
When it is driving a load, the decoupling must be arranged to ensure 
that the total loop in which the load current flows is as small as possible. 
Figure 9-15 shows an emitter follower without supply decoupling — ^the 
HF current in the load must flow through the power supply to return to 
the output stage (remember that Kirchoff 's Law says, in eflfect, that cur- 
rents must flow in circles). Figure 9-16 shows the same circuit with 
proper supply decoupling. 

TTiis principle is easy enough to apply if the load is adjacent to the 
circuit driving it. Where the load must be remote it is much more diffi- 
cult, but there are solutions. These include transformer isolation and the 
use of a transmission line. If the signal contains no DC or LF compo- 



Rgufed-tS. 



DECOUFLH^G 



PfoportydeooupiBd 

iOCBllOOd 



Constant 
Current A 
Source ^ 



S7 



Load 



112 



James M. Bryant 



nents, it may be isolated with a transformer close to the driver Such an 
arrangement is shown in Figure 9-17. (The nature of the connection from 
the transformer to the load may present its own problems — ^but supply 
decoupling is not one of them.) 

A correctly terminated transmission line constrains HF signal currents 
so that, to the supply decoupling capacitors, the load appears to be adja- 
cent to the driver Even if the line is not precisely terminated, it will con- 
strain the majority of the return current and is frequently sufficient to 
prevent ground current problems. 



DECOUPLING WITH REMOTE LOAD 



Figure 9-17. 



Constant 

Current 

Source 




TO REMOTE 
OUTPUT 



DECOUPLING WITH REMOTE LOAD 



Figure 9-18. 



Constant 
Current y 



Go^ Una Id Load 



Breacttjoarding Principles 

Having considered issues of resistance, capacitance, and inductance, it is 
clear that breadboards must be designed to minimize the adverse effects 
of these phenomena. The basic principle of a breadboard is that it is a 



113 



Analog Breadboarding 



temporary structure, designed to test the performance of a circuit or sys- 
tem, and must therefore be easy to modify. 

There are many commercial breadboarding systems, but almost all 
of them are designed to facilitate the breadboarding of digital systems, 
where noise immunities are hundreds of millivolts or more- (We shall 
discuss the exception to this generality later.) Matrix board (Veroboard, 
etc,)* wire-wrap, and plug-in breadboard systems (Bimboard, etc) are, 
without exception, unsuitable for high performance or high frequency 
analog breadboarding. They have too high resistance, inductance and 
capacitance. Even the use of IC sockets is inadvisable* (All analog engi- 
neers should practice the art of unsoldering until they can remove an IC 
from a breadboard [or a plated-through PCB] without any damage to the 
board or the device — solder wicks and solder suckers are helpful in ac- 
complishing this,) 

Practical Breadboarding 

The most practical technique for analog breadboarding uses a copper- 
clad board as a ground plane. The ground pins of the components are 
soldered directly to the plane^ and the other components are wired to- 
gether above it. This allows HF decoupling paths to be very short indeed. 
All lead lengths should be as short as possible, and signal routing should 
separate high-level and low-level signals. Ideally the layout should be 
similar to the layout to be used on the final PCB. 

Pieces of copper-clad may be soldered at right angles to the main 
ground plane to provide screening, or circuitry may be constructed on 
both sides of the board (with connections through holes) with the board 
itself providing screening. In this case the board will need legs to protect 
the components on the underside from being crushed. 



Rgure 9-19, 




James M. Bryant 




Figure 9-20. 

When the components of a breadboard of this type are wired point- 
to-point in the air (a type of construction strongly advocated by Robert A. 
Pease of National Semiconductor^ and sometimes known as "bird*s nest" 
construction) there is always the risk of the circuitry being crashed and 
resulting short-circuits; also, if the circuitry rises high above the ground 
plajie, the screening effect of the ground plane is diminished and interac- 
tion between different parts of the circuit is more likely. Nevertheless the 
technique is very practical and widely used because the circuit may so 
easily be modified. 

However, there is a conunercial breadboarding system which has most 
of the advantages of "biiti's nest over a ground plane** (robust ground, 
screening, ease of circuit alteration* low capacitance, and low inductance) 
and several additional advantages: it is rigid, components are close to the 
ground plane, and where necessary node capacitances and line imped- 
ances can be calculated easily. This system was invented by Claire R. 
Wainwright and is made by WMM GmbH in the town of Andechs in 
Bavaria and is available throughout Europe and most of the world as 
''Mini-Mount" but in the USA (where the trademark **Mini-Mount" is the 
property of another company) as the "Wainwright Solder-Mount Sys- 
tem."^ (There is also a monastery at Andechs where they brew what is 
arguably the best beer in Germany.) 

Solder-Mounts consist of small pieces of PCB with etched patterns on 
one side and contact adhesive on the other They are stuck to the ground 
plane and components are soldered to them. They are available in a wide 



Analog Breadboarding 



variety of patterns, including ready-made pads for IC packages of ail 
sizes from 8-pin SOICs to 64-pin DILs, strips with solder pads at inter- 
vals (which intervals range from ,040" to .25"; the range includes strips 
with O.r* pad spacing which may be used to mount DIL devices), strips 
with conductors of the correct width to form microstrip transmission 
lines (50i2, 60fl, 15SI or lOOQ) when mounted on the ground plane, and 
a variety of pads for mounting various other components. A few of the 
many types of Solder-Mounts are shown in Figure 9-20. 

The main advantage of Solder-Mount construction over **bird's nest" 
is that the resulting circuit i% far more rigid, and, if desir^, may be made 
far smaller (the latest Solder-Mounts are for surface-mount devices and 
allow the construction of breadboards scarcely larger than the final PCB, 
although it is generally more convenient if the prototype is somewhat 
larger). Solder-Mounts are sufficiently durable that they may be used for 
small quantity production as well as prototyping — ^two pieces of equip- 
ment I have built with Solder-Mounts have been in service now for over 
twenty years. 

Figure 9-21 shows several examples of breadboards built with the 
Solder-Mount System. They are all HF circuits, but the technique is 
equally suitable for the construction of high resolution LF analog cir- 
cuitry. A particularly convenient feature of Solder-Mounts at VHF is the 
ease with which it is possible to make a transmission line. 

If a conductor runs over a ground plane it forms a microstrip transmis- 
sion line. The Solder-Mount System has strips which form naicrostrip 
lines when mounted on a ground plane (they are available with imped- 
ances of 50Q, 60Q, 15Q and lOOfi). These strips may be used as trans- 
mission lines, for impedance matching, or simply as power buses. (Glass 
fiber/epoxy PGB is somewhat lossy at VHF and UHF, but the losses will 
probably be tolerable if microstrip runs are short.) 

It is important to realize that current flow in a microstrip transmission 
line is constrained by inductive effects. The signal current flows only on 
the side of the conductor next to the ground plane (its skin depth is calcu- 
lated in the normal way) and the return current flows only directly beneath 
the signal conductor, not in the entire ground plane (skin effect naturally 
limits this current, too, to one side of the ground plane). This is helpful in 
separating ground currents, but increases the resistance of the circuit. 

It is clear that breaks in the ground plane under a microstrip line will 
force the return current to flow around the break, increasing impedance. 
Even wdrse^if the break is made to allow two HF circuits to cross, the 
two signals will interact. Such breaks should be avoided if at all possible. 
The best way to enable two HF conductors on a ground plane to cross 
without interaction is to keep the ground plane continuous and use a mi- 
crostrip on the other side of the ground plane to carry one of the signals 
past the other (drill a hole through the ground plane to go to the other 
side of the board). If the skin depth is much less than the ground plane 
thickness the interaction of ground currents will be negligible. 



116 



James M. Btyant 




Figure 9-22. 



MICROSTRIP TRANSMtSSrON LINE 

(cufiwit flow nofnud 
to piMieotdlaomn) 




HFilgnal&fttum 

currents kTonltood 

When a conductor runs over a ground plane it forms a tnicrostrip transmission line, 
377H 



The characteristic impedance is 



wViT 



n (note that the units of H and W are unimportant) 



The traiKraission line determines where both the signal and return currents flow 



117 



Analog Breadboarding 



Conclusion 

It is not possible in a short chapter to discuss all the intricacies of suc- 
cessful analog teeaulboardconstoiction/te 

principle is to remember all the laws of nature which apply and consider 
their effects on the design. 



Figure 9-23. 



SIK^ES^y L AH ALOG Bf^MlBMftf:^ 

Pay attention to: 
Resistance 
Capacitance 
Induetance 
Decoupiing 
Ground 
& 

Separating sensitive circuits from noisy ones 



In addition to the considerations of resistance, skin effect, capacitance, 
inductance and ground current, it is important to configure systems so 
that sensitive circuitry is separated from noise sources and so that the 
noise coupling mechanisms we have described (common resistance/in- 
ductance, stray capacitance, and mutual inductance) have minimal oppor- 
tunity to degrade system performance. ("Noise" in this context means a 
signal we want [or which somebody wants] in a place where we don't 
want it; not natural noise like thermal, shot or popcorn noise.) The gen- 
eral rule is to have a signal path which is roughly linear, so that outputs 
are physically separated from inputs and logic and high level external 
signals only appear where they are needed. Thoughtful layout is impor- 
tant, but in many cases screening may be necessary as well. 

A final consideration is the power supply. Switching power supplies 
are ubiquitous because of their low cost, high efficiency and reliability, 
and small size. But they can be a major source of HF noise, both broad- 
band and at frequencies harmonically related to their switching 
frequency. This noise can couple into sensitive circuitry by all the means 
we have discussed, and extreme care is necessary to prevent switching 
supplies from ruining system performance. 

Prototypes and breadboards frequently use linear supplies or even 
batteries, but if a breadboard is to be representative of its final version it 
should be powered from the same type of supply. At some time during 



118 



James M. Bryant 



Figure 9-^4, 



Generate noise at every frequency under the 
Sun (and some interstellar ones as well). 

Every mode of noise transmission is present: 



ff you must use them you should filter, screen, 
ke^ them far away from sensitive circuits, 
and still worry! 



development, however, it is interesting (and frightening, and helpful) to 
replace the switching supply with a battery and observe the difference in 
system performance. 

Rgure9-*25. 



OBEY THE LAW 

Unexpected l)ehaviour of analog circuitry is almost always due to the 
designer overlooking one of the basic laws of electronics. 
Remember and obey Ohm, Faraday, Lenz, Maxwell, Kirchoff 

and MURPHY. 

"Muiphy always was an optimtst" - Mrs, Murphy. 



RefBrences 



1 . Robert A. Pease, Troubleshooting Analog Circuits (Butterworth-Heinemann, 199 1 ). 

2. Wainwright Instruments Inc., 7770 Regents Rd., #1 1 3 Suite 371 , San Diego, CA 

92122 (619) 55S 1057 Fax: (619) 558 1019. 

WMM GmbH, Wainwright Mini-Mount-System, HartstraBe, 28C, D-82346 
Andechs-Ftieding, Germany, (+49)8152-3162 Fax: (+49)8152-4025. 



119 



This page intentionally left blank 



Carl Battjes 



10. Who Wakes the Bugler? 



Introduction: T-Coils in Oscilloscope Vertical Systems 

Few engineers realize the level of design skill and the care that is needed 
to produce an oscilloscope, the tool that the industry uses and trusts. To 
be really effective, the analog portion of a vertical channel of the oscillo- 
scope should have a bandwidth greater than the bandwidth of the circuit 
being probed, and the transient response should be near perfect. A verti- 
cal amplifier designer is totally engrossed in the quest for this unnatural 
fast-and-perfect step-response. The question becomes, "How do 'scope 
designers make vertical amplifier circuits both faster and cleaner than the 
circuits being probed?" After all, the designers of both circuits basically 
have the same technology available. 

One of many skillful tricks has been the application of precise, spe- 
cial forms of the T-coil section. I'll discuss these T-coil applications in 
Tektronix oscilloscopes from a personal and a historical perspective, and 
also from the viewpoint of an oscilloscope vertical amplifier designer. 
Two separate stand-alone pages contain "cookbook" design formulas, 
response functions, and related observations. 

The T-coil section is one of the most fun, amazing, demanding, capa- 
ble, and versatile circuits I have encountered in 'scopes. Special forms Figure 10-1. 

The T-coil Section. 



L = END TO END INDUCTANCE 
T 

C C 




121 



Who Wakes the Bugler? 



of this basic circuit block are used with precision and finesse to do the 
following: 

Peak capacitive loads 
Peak amplifier interstages 
Form "loop-thru" circuits 
Equalize nonlinear phase 

Transform capacitive terminations to resistive terminations 
Form distributed deflectors in cathode ray tubes 
Form artificial delay line sections 
Form distributed amplifier sections 

I have successfully used T-coils in all of these applications except the 
last two. Recently, however, some successful designers from the '40s and 
'50s shared their experiences with those two applications. 



Over My Head 

While on a camping trip in Oregon in 196 1,1 stopped at Tektronix and received an 
interview and a job offer the same day. Tektronix wanted me. They were at a stage 
where they needed to exploit transistors to build fast, high-performance 'scopes. I 
had designed a 300MHz transistor arTq>)ifter while worlang at Sylvania. In 1961 , 
that type of experience was a rare commodity. Actually I had designed a wide- 
band 300MHz IF amplifier that only achieved 200MHz. What we (Sylvania) used 
was a design that nry technician came up with that made 300MHz* So I anived at 
this premier oscilloscope company feeling somewhat of a fiaud. I was more than 
just a bit intimidated by the Tektronix reputation and the distributed amplifiers and 
artificial delay lines and alt that "stuff" that really worked The voltage dynamic 
range, the transient response cleanliness, and DC resp^^ requirements for a 
vertical output amplifier made my low-power, 50 Ohm, 300MHz IF amplifier seem 
like child's play Naturally, I was thrown immediately into the job of d^^iing high- 
bandwidth oscitk)scope transistor vertical-output ampiiers. I fell tike a pri^te, 
fresh out of bask: training, on the front lines in a war. 



The Two Principles of Inductive Peaking 

The primary and most obvious use of a T-coil section is to peak the fre- 
quency response (improve the bandwidth, decrease the risetime) of a 
capacitance load. Inductances, in general, accomplish this through the 
action of two principles. 

Principte Number One: Separate, in Time, the Charging of C^n^itences 

The coaxial cable depicts a limiting case of Principle Number One. A 
coaxial cable driven from a matched-source impedance has a very fast 
risetime. The source has finite resistance and the cable has some total 
capacitance. If the cable capacitance and inductance are uniformly distrib- 



122 



Car! Battles 



T 



jr^Y^ — — 

PEAKtMG 

CAf»ACITANCE LOAD 





DISTRIBUTE 



1LA.A-AJt ■ : %A.A.A^ 



D AHMIFXEII 



1 



AR 



I F I C I At 



DELAY I I ME 



S I GNAL> 




S I & N A L 




llfil^AL ^ 



TAP — TAP 

SI6MAL LOOP THRU 



T E RM iiiATX^pr Fixri^ 

ar y 



_<R CRT DISTRIBUTED DEFLECTOR 



(source or load) 

! 





Figure 10-2. 

TheVefsatileT-coil. 



uted and the cable is situated in the proper impedance environment, the 
bandwidth is » l/lTtRQawe and the risetime « 2.2 RQ^bie- The distrib- 
uted inductance in the line has worked with the distributed capacitance to 
spread out, in time, the charging of this capacitance. A pi-section LC 
filter could also demonstrate Principle Number One, as could a distrib- 
uted amplifier. 



123 



Who Wakes the Bugler? 



Figure 10-3. Separate, In Time, the Charging of Capacitances. 
Peaking Principle 1 




Principle Number l^vo: Don't Waste Current Feeding a Restetor WHen a 
Capacitor Needs to Be Charged In Figure 1(M a helpftil elf mans the 
normally closed switch in series with the resistor. When a current step 
occurs, the elf opens the switch for RC seconds, allowing the capacitor to 
take the full current. After RC seconds, the capacitor has charged to a 
voltage equal to IR. The elf then closes the switch, allowing the current 




Figure 1(M. 

Don't Waste Time Feeding a Resistor When a Capacitor Needs to be Charged. 

Peaking Principle 2 

124 



to feed the resistor, also producing a voltage equal to IR. No current is 
wasted in the resistor while the capacitor is charging. 

A current step applied to the constant-resistance bridged T-coil yields 
the san^ capacitor voltage risetime, 0.8 RC, as the elf circuit. In both 
cases, during the rise of voltage on the capacitor, the voltage waveform 
on the termination resistor is negative, zero, or at least low. Without the 
helpful elf, or without the T-coil, the risetime would have been 2.2 RC. 
With these risetime enhancers, the risetime is lowered to 0.8 RC. This is 
a risetime improvement factor of 2.75. If there are two or more capacitor 
lumps. Principle Number One can combine with Principle Number Two 
to obtain even higher risetime improvement factors. 

When both principles are working optimally, reflections, overshoot, 
and ringing are avoided or controlled. This is a matter of control of en- 
ergy flow in and out of the T-coil section reactances. A T-coil needs to be 
tuned or tolerated. In the constant-resistance T-coil section, given a load 
capacitance, there is only one set of values for the inductance, mutual 
inductance, and bridging capacitance which will satisfy om set of speci- 
fications of the driving point resistance (may imply reflection coefficient) 
and desired damping factor (relates to step response overshoot). 

T-C^ Peaking C^Meitance Loads 

A cathode ray tube (CRT) electrostatic deflection plate pair is considered 
a pure capacitance load. In the '50s and '60s, T-coils were often used in 
deflection plate drive circuits. Usually a pentode-type tube was used as 
the driver, rather than a transistor, because of the large voltage swing 
required. The pentode output looked like a capacitive high-impedance 
source. A common technique was to employ series peaking of the driver 
capacit^ce, cascaded with T-coiled CRT deflection plate capacitance. 



The 10-MHz Tektronix 3 A6 

The 3A6 vertical deflection amplifier works really hard. The 3A6 ptugnn was de- 
signed to operate in the 560 series mainframes, where the plug-ins drove the 
CRT deflection plates directly. The deflection sensitivity was poor (20 volts per 
dimkm) imd the capa^anoe was high. To cover the di^ajNNBMWfl Nnearly m6 
allow sufficient overscan, the output beam power tube on each side had to tra- 
verse at least 80 volts. The T-coils on the 3A6 made the bandwidth and dynamic 
range possible without burning up the large output vacuum tubes. 



A i^l^Coff Response 

A vertical-output deflection-amplifier designer has a unique situation— 
the amplifier output is on the screen — no other monitor is needed. This 
is the case with the 3A6 circuit shown here. The input test signal is clean 
and fBSt, The frequency and step response of the entire vertical system 
is dominated by the "tuning" of the T-coil L384 and its opposite-side 



Who Wakes the Bugler? 




Figure 10^. 

Step Response Waveforms 3A6 Tcoil Peaking. 
126 



Carl Battjes 



FACT SHEET FOR 
CONSTANT-RESISTANCE T-COILS 



L - END TO END INDUCTANCE 




dain piiip; fac tor 
2 ' (i-k) 



Lt =s 2L + 2M 
If 



M 



k=coupUng coefficient /c^ ^jand Zt^2(1h^ 



Lr=i?^C and Cs =^ 



Then 
and 

and 



VI 

i 



=7? the Constant Resistance Property 

R 



RCs {\-k)R^cV 
2 4(l+jt) 



a Quadratic (2 pole) Response at \2 



2 4(l+fc) 



RCs i\-k)R^c\^ 
2 4(1+A:) 

V2 Step response overshoot 

k= .6 (CRITICAL DAMPING) 0.0% 

k=.5 (FLAT DELAY) 0.4% 

k=333 (FLAT AMPLITUDE) 43% 

k= 0.0 ( high frequency DELAY BOOST ) 16.0% 

SPECIAL NOTE ON m-DERlVED T-COILS. 
ThgTtelYfdfrfiil ^se from m^derived filter tlieofy* They tfff m% \M sm^mH^kW^ 
property; The tot^l tndiietaiice R C. Tbejr have no bddgjk^ capacitance. Hiey do not have a simple 



an ALL PASS response at \3 



quadratic (Z pote) response. The value of "m" implies a couplimtcoefricient ^ 



Rgure10-€. 

Fact Sheet on Constant Resistance T-coils. 



127 



Who Wates the Bugler? 



counterpart. The bottom picture shows the response when the coils (L384 
and its mate) were disabled. ( AH three terminals of each coil were 
shorted together.) This reveals that, without the coils, the response looks 
very much like a single-time-constant response. The middle picture illus- 
trates the progression of tuning after the shorts are removed. The pow- 
dered iron slugs in the coil forms are adjtisted to optimize tiie response. 
The top picture shows the best response. The l O-to-90% risetime of the 
beginning waveform is 75 nanoseconds, and in the final waveform it 
drops to 28 nanoseconds. This is a ratio of risetimes of 2,6 — near the 
theoretical bandwidth improvement factor of 2.74. The final waveform 
has peak-to-peak aberrations of 2%. 

The total capacitance at the deflector node includes the deflection 
plates, the wires to the plates, the beam power tube plate capacitance, the 
wiring and coil body capacitance, the plug-in connector capactfaiQce, the 
mounting point capacitances, the chassis feedthrough capacitance, the 
resistor capacitance, and possibly virtual capacitance looking back into 
the tube. We can solve for the equivalent net capacitance per side by 
working back from the 75nsec risetime and the 1.5k load resistance. This 
yields about 23pF per side. Although each coil is one solenoidal winding, 
it actually performs as two coils. The coil end connected to the tube plate 
works as a series peaking coil, and the remainder as the actual T-coil. 

L344, which is also a T-coil, appears upstream in the 3A6 schematic 
fragment. Notice that the plate feeds the center tap of this coil. This is an 
application of reciprocity (Look in your old circuit textbook!). If the 
driving device output capacitance is significantly greater than the load 
capacitance, it may be appropriate to use this connection. 



Distributed Amplifiers in Oscilloscopes 

The idea of a distributed amplifier goes back to a Britisii "Patent Specification" by 
W.S. Percival in 1936. In August 1948, Ginzton, Hewlett, Jasberg, and Noe pub- 
lished a classic paper on distributed amplifiers in the 'Proceedings of IRE " At ^oiA 
the same time, Bill Hewlett (yes, of HP) and Logan Belleville (of Tektronix) met at 
Yaws Restaurant in Portland. Bill Hewlett described the new distributed amplifier 
concepts (yes, he "penciled ouF the idea on a nspkin!). In 1 948, from Au^ 
through October, Howard Vollum and Richard Rhiger built a distributed amplifier 
under a government contract. This amplifier was intended for use in a high-resolu- 
tion ground radar. It had about a 6nsec risetime and a hefty output swing. In order 
to measure the new amplifier's performance, Vollum and Rhiger haif onboard^ it 
on the side of an early 51 1 'scope, directly feeding the deflectors. 

It soon became clear that what the government and industry really needed 
was a very fast oscilloscope. I am not sure of the details or sequence of events, 
but Tektronix— Howard Vollum's two-year-old company—was making history. 
Vollum, Belleville, and Rhiger developed the 50MHz 517 oscilloscope, an oscillo- 
scope with a distributed amplifier in the vertical d^lection path. Vollum and 
Belleville had successfully refined the distributed amplifier enough to satisfy this 
oscilloscope vertical amplifier application. The product was successful and order 



128 



Carl Batties 




figure 10-7. 

1948 Experiment— 
Outboarded 
Distributed 
Amplifier. 



rates exceeded Tek's ability to manufacture. Logan left Tektronix in the early *50s 
and Voflum and Rhiger were left managing this new big company. John Kobbe, 
Cliff Moulton, and Bill Polits, as well as other key electrical circuit designers, took 
up where Vollum, Belleville, and Rhiger had left off. Other distributed amplifiers 
were designed for other 'scopes during the '50s, including the 540 series at 
30MH2 and the 580 series at 100MHz. 



Manufacturing Distributed Amplifier Oacilioscopes 

The whole idea of using a distributed amplifier as an oscilloscope vertical 
amplifier is rather incredible to me. Obtaining a very fast, clean step re- 
sponse is a hard job. When T-coils are employed, the job is even harder 
When they are employed wholesale, as in a distributed amplifier, they are 
"fussy squared or tripled.** The tuning of an oscilloscope distributed am- 
plifier and/or an artificial delay line is tricky. l\ining is done in the time 
domain* with clues about where and in which direction to adjust, coming 
from observations of the "glitches" in the step response. If the use of a 
distributed amplifier in the vertical channel of an oscilloscope was pro- 
posed in today's business climate, it would be declared *'un manufacture 
able.'* It would never see the light of day. However, the Tektronix boom 
expansion in the '50s occurred largely through the development, manu- 
facture, and sale of distributed amplifier 'scopes. 

The lOOMHz 580 series was the last use of distributed amplifiers in 
Tektronix *scope vertical systems. EHjal triodes, low cathode connection 
inductance, cross-coupled capacitance neutralization, and distributed 
deflectors in the CRT helped to achieve this higher bandwidth. 




Figure 10^. 

Tektronix 585 Distributed Amplifier Vertical Output. 



Distributed Deflector for a Cathode Ray Tube 



In 1961, CliflF Moulton's IGHz 519 'scope led the bandwidth race. This 
instrument had no vertical amplifier. The input was connected to a 
1 25-ohm transmission line which directly fed a single-ended distributed 
deflection system. Schematics in Figures 10-8 and 10-9 show somewhat 
pictorially what a distributed deflector looks like. The 519 deflector is not 
.shown. Within the CRT envelope was a meander line distributed deflec- 
tion plate. Tuning capacitors were located at the sharp bends of the mean- 
der line. The line was first tuned as a mechanical assembly and later 
incorporated into the CRT envelope. 

Terminated distributed deflector structures create a resistive driving- 
point impedance in place of one lumped capacitance. They also synchro- 
nize the signal travel along the deflection plate to the velocity of the 
electron beam speeding through the deflection plate length. If a distrib- 
uted deflector is not used, deflection sensitivity is lost at high frequency 
due to transit time. Relative sensitivity is 

. / 
sin— 

X where f is fr^uency and ft^ is an inverse transit time fimction. 

This is usually significant at lOOMHz and above, and therefore dis- 
tributed deflectors show up in 'scopes with bandwidths of lOOMHz or 
higher. Various ingenious structures have been used to implement distrib- 
uted deflectors. All could be modeled as assemblies of T-coils. The effec- 
tive electron beam deflection response is a function of all of the T-coil tap 
voltages properly delayed and weighted. 

Theoretical and Pragmatic Coii Proportions 

The basis for the earliest T-coil designs was m-derived* filter theory. The 
delay lines and the distributed amplifier seemed to work best when the 
coils were proportioned — as per the classic Jasberg-Hewlett paper^— at 
m = 1 .27 (coupling coefficient = 0.234). This corresponds to a coil length 
slightly longer than the diameter. In the design phase, there was an in- 
telligent jugghng of coil proportions based on the preshoot-overshoot 
behavior of the amplifier or delay line. The trial addition of bridging 
capacitance invariably led to increased step response aberrations. 



1 . m-dejived filters were outeonies of image-parameter filter theory of the past. The parameter "m' 
detennined the shape of the amplitude and phase response. "m"=1.27 approximated flat delay 
response. Filters could not be exactly designed, using this theory, because the required termina- 
tion was not realizable. 

2. This classic paper described both the m-derived T-coil seetion and, very briefly, the constant- 
resistance T-coil section. The use of these sections in distributed amplifiers was the main issue 
and nothing was mentioned of other uses. 



Who Wakes the Bugler? 



In contrast with the artificial delay lines and the distributed amplifiers, 
the individual peaking applications usually needed a coil with more cou- 
pling (k = 0.4 to 0.5), which was realized by a coil shorter than its diame- 
ter. When the coil value is near or below 100 nanohenries, the goal is 
then to get as much coupling as possible so that the lead inductance of 
the center tap connection can be overcome. Flat pancake or sandwich 
coils of thin PC board material, thin films, or thick films are used to 
achieve high coupling. 



The Importance of Stray Cipaot^ce in T^^H 

The stray interwinding capacitance of a T-coil can be crudely modeleci by 
one bridging capacitance C^s across the whole coil. It is defined by the 
coil self-resonance frequency "f«> " 

c - ^ 

where Lj is the coil total inductance. If is the required bridging capaci- 
tance for constant-resistance proportions, then Cx=Cb-Cbs needs to be 
added. This is an effective working approximation. The recent coils built 
for high-frequency 50 Ohm circuits usually need additional bridging ca- 
pacitance. On the other hand, the old nominally m-derived circuits never 
needed any added bridging capacitance. They were high-impedance cir- 
cuits with very large coils and probably had enough effective bridging 
from the stray interwinding capacitance. Hiey were probably constant- 
resistance coils in disguise. Capacitance to ground of the coil body is al- 
ways a significant factor also. 



interstage Peaking 

The Tektronix L and K units of the '50s were good examples of inter- 
stage T-coil peaking. The T-cpils were used to peak, not the preamp input 
or the output, but in the middle of the amplifier. The interstage bandwidth 
was boosted well above the 



InRiCtotai gain InCtotai gain InCsubtotai gain 

The individual pre-amp bandwidths are 60MHz. This is amazing be- 
cause the effective of the tiri>es was only 200MHz or so. Both inductive 
peaking and f^ doubling techniques were needed to "hot rod" these plug- 
ins to this bandwidth. 



132 



Carl Battles 



T-Coils in Transistor Interstages 

The 1 50MHz 454 evolved from ttie 50MHz 453 oscilloscope by adding distrtouted 
deflection plates to the cathode ray tube and, among other things, using a new 
output amplifier This an^lif ier employed T-coil peaking in the interstages. The T- 
coil design was based on a lossless virtual capacitance, a very big approxtn^ation. 
This virtual capacitance at the base was dominated by the transformation of the 
emitter ieedback admittance into the base. The emitter feedback cascode connec- 
tion made two transistors function more like a pentode. The initial use of transis- 
tors in the early '60s showed us that most of the time, vacuum tube techniques 
dkln't work with Those blasted transistors.'* After all, vacuum tubes had a physical 
capacitance that was measurable on an "off" tube; transistors had this Virtual 
capacitance thing^! The conventional thinking in the design groups at Tek in the 
early and mid '60s was that inductive peaking and transistor high-fkleiity pulse 
amplifiers were not compatible. Despite this, the T-coils and transistors did work, 
the 454 worked, and the 454 was a "cash cow" for Tektronix for several years. 
Since then, ICs have displaced discrete transistors and the 'scope bandwidths 
translated upwards, with and without T-coils. The fastest amplifiers, however, are 
always produced wrfh the aid of some T-coil configuration. 



Ffgure10-9, 

Tektronix 454 
VerticahOutput 
Amplifier and 
Interstage T-K^oil. 




WhoWakes the Bugler? 



Phase Compensation wifh T-CoUs 

The portable 453 needed a compact delay line for the vertical system that 
didn't require tuning. Kobbe had designed and developed a bidanced- 
counterwound delay line for the 580 series of 'scopes. We made it still 
smaller. This delay line worked well at 50MHz, and had reasonably low 
loss at 150MHz. Unfortunately, the step response revealed a preshoot 
problem. The explanation in the frequency domain is nonlinear phase 
response. High-frequency delay was insufficient, and one could see it as 
preshoot in the step response. Three sections of a constant-resistance- 
balanced T-coil structure added enough high-frequency delay to clean up 
the preshoot, and even speed the risetime by moving high frequencies 
into their "proper time slot." T-coil sections can provide delay boost at 
high frequencies if the T-coil section is proportioned differently from that 
of ttie peaking application. A negative value for "k" is usually appropri- 
ate and is realized by adding a separate inductor in the conmion leg. 



Integrated Circuits 

In the late '60s, when the 454A was being developed, George Wilson, head of 
the new Tektronix Integrated Circuits Group at that time, wanted to promote the 
design of an integrated circuit vertical ampHfier. I rebuffed him, saying, can 
never use ICs in vertical amplifiers because they have too much substrate capac- 
itance, too much collector resistance, and too low an ft" I was correct at the time, 
but dead wrong in the long run. In the 70s, Tektronix pushed fC dev^pment in 
parallel with the high-bandwidth 7000 series oscilloscopes. 




134 



I stopped my slide into obsolescence in 1971 by doing a little downward mobil- 
ity. I left the smalt portable oscilloscope group I headed, and joined George Wilson 
in the IC group as a designer. This foresight on my part was nrvost uncharacteristic. 



T*Coils with Inl^irateGl Circuit V^rttcirt Ampltfiers 

The initial use of integrated circuits in the vertical amplifiers of Tektronix 
'scopes supplied a huge bandwidth boost, but not just because of the high 
f^. New processes included thin film resistors that allowed designers to 
put the small value emitter feedback resistors on the chip, thus eliminat- 
ing the connection inductance in the emitters of transistors. That emitter 
inductance had made a brick wall limit in bandwidth for discrete transis- 
tor amplifiers. That wall was pretty steep, starting in the 150~200MHz 
area. In order to have flat, non ripple, frequency response at VHP and 
UHF, the separately packaged vertical amplifier stages needed to operate 
in a terminated transmission line environment. T-coils were vital to 
achieve this environment. Thor Hallen derived formulas for a minimum 
VSWR T-coil. Packaging and bond wire layout made constant-resistance 
T-coil design impossible. Hallen's T-coil incorporated and enhanced the 
base connection inductance. The Tektronix 7904 achieved 500MHz 
bandwidth by using all of the above, along with 3GHz transistors and 
an ft-doubler amplifier circuit configuration. 

In 1979, the IGHz 7104 employed many of the 7904 techniques but, 
in addition, had 8GHz f^ transistors, thin film conductors on substrates, 
and a package design having transmission line interconnects. It also had 
a much more sensitive cathode ray tube. Robert Ross had eariier devel- 
oped formulas for a constant-resistance T-coil to drive a non-pure capaci- 
tor (a series capacitor-resistance combination). John Addis and Winthrop 
Gross made use of the Ross type T-coils (patterned with the thin film 
conductor) to successfully peak the stages and terminate the inter-chip 
transmission lines, 

I have lumped Thor Hallen's and Bob Ross's T-coils together in a class 
I call "lossy capacitor T-coils." 

Dtial OMr^ wRh fCoils 

In 1988, the digitizing IGHz Tektronix 11402 was introduced. A fast 
real-time cathode ray tube deflection amplifier was no longer needed. 
T^ite were employed, however, m the 1 1 A72 dual-channel plug-in pre- 
amp hybrid (Figure 10-12), where all of the two-channel analog signal 
processing took place. The T-coils peaked frequency response and mini- 
mized input reflections in the 50 Ohm input system. As in the 7904 
'scope, Hallen used a design technique for the T-coils that minimized 
VSWR. To realize this schematic, a T-coil was needed which had 



Who Walffis the Bugler? 



Tw© Types of Lossy CapN^or T-colis 



ROSS CONSTANT-RESISTANCE T-GOIL 




rIc „ . 



Lti= 



Cb = 



2 

166^^ Rl^ 



d^dmtpingfactor of quadratic response 



VI 

/ 

V2 



=J?L The Constant-Resistance property 

Rl 



Two Pole Response 



HALLEN MINIMUM VSWRT-CGIL 



For the Hallen and the Ross T-coils 

As Rb gets bigger,the input coil inductance 
gets smaller* 

With a finite Rb» the response at RL is not 

5S 




L,ofa/=i?i[-p^+(|^+l)Cc] 

J _ Lmal . . J_ . ReCcTt(Rc-^2RB) IRsTt+ReRcCc 

^ 2^' RL\T,^R,Cc^R,Ccf T^t^^eCc^RcCc^^ 
L2=Ltatal-Li 

rI {Tt^ReCc^RcCcXLi+Li) Tt+ReCc-^RcCc Li+Li ^ 



FigumlMI. 

Two Types of Lossy 
Capacitor T-coils. 



136 



Carl Battjes 



enough mutual inductance to cancel the bond wire inductance that 
would be in series with its center tap. The remaining net branch induc- 
tances then had to match Hallen's values. To guide the physical layout 
of this coil, I used a three-dimensional inductance calculation program. 
This program was used iteratively. The two '*G*' patterns on the multi- 
layer thick film hybrid are the top layer of these input T-coils. The major 
dimension of these coils is 0.05 inches. In between the chips are coils 
which **tune out** the collector capacitance of the transistor of each out- 
put channel. These coils are formed by multiple-layer runs and bond 
wire "loopbacks.'' 

Afterglow 

Conspfcuous by its absence is a discussion of wideband ampUfier config- 
urations and how they operate* I have referred to f^-doublers and current 
doublers without explanation. I had to really restrain myself to avoid that 
topic for the sake of brevity. The ultimate bandwidth limit of high-fidelity 
pulse amplifiers depends on the power gain capability (expressed by an 
fjvjAx^ for example) of the devices, and the power gain requirements of the 
amplifier. To approach this ultimate goal requires the sophisticated use of 
inductors to shape the response. For bipolar transistors, the f^-doubler 
configurations and smgle-stage feedback amplifiers, combined with in- 
ductive peaking, do a very good job. 

I hope this chapter has raised your curiosity about the circuit applica- 
tions of the T-coil section. I have not written this chapter like a textbook 




Figure 10-1Z 

11A721.5GH2 
Muttitay@f Hybrid 
withThfGk Film 
T<;oils. 



Who Wakes the Bugler? 



and I am hoping that my assertions and derivation results are challenged 
by the reader. To get really radical, breadboard a real circuit! A less fun 
but easier way to verify circuit behavior is via SPICE or a sinular sintiula- 
tor program. Keep in mind, while you are doing this, that most of the 
very early design took place without digital computer simulators. 
Frequency- and impedance-scaled simulations took place though, with 
physical analog models. 

Fm grateful to the many knowledgeable folks who talked with me 
recently and added considerable information, both technical and histori- 
cal. These included Gene Andrews, Phil Crosby, Logan Belleville, Dean 
Kidd, John Kobbe, Jim Lamb, Cliff Moulton, Oscar Olson, Ron Olson, 
and Richard Rhiger. If this chapter has errors, however, don't blame these 
guys; any mistakes are my own. 

Bob Ross and Thor Hallen have been sources of insight on these top- 
ics over many years and have been ruthless in their rigorous analyses, 
helping me in my work immensely. 

Finally, I leave you with my mother's and Socrates' advice, 
"Moderation in all things." Might I add, "Just do it!" If these Tek guys 
had waited for proper models of all known effects and proper theory 
before doing something, we would still be waiting. Everything can be 
tidied up in hindsight but, in fact* the real circuits in the real products are 
often more complicated than our simple schematics and were realized by 
a lot of theory, intuition, and especially smart, hard, and sometimes long 
work. I am proud of all of this heritage and the small part I played in it. 



138 



Jim Williams 



1 1 . Tripping the Light Fantastic 



Introduction 

Where do good circuits come from, and what is a good circuit? Do they 
only arrive as lightning bolts in the minds of a privileged few? Are they 
synthesized, or derived after careful analysis? Do they simply evolve? 
What is the role of skill? Of experience? Of luck? I can't answer these 
weighty questions, but I do know how the best circuit I ever designed 
came to be. 

What is a good circuit, anyway? Again, that's a fairly difficult question, 
but I can suggest a few guidelines. Its appearance should be fundamen- 
tally simple, although it may embody complex and powerful theoretical 
elements and interactions. That, to me, is the essence of elegance. The 
circuit should also be widely utilized. An important measure of a circuit's 
value is if lots of people use it, and are satisfied after they have done so. 
Finally, the circuit should also generate substantial revenue. The last time 
I checked, they still charge money at the grocery store. My employer is 
similarly faithful about paying me, and, in both cases, it's my obligation 
to hold up my end of the bargain. 

So, those are my thoughts on good circuits, but I never addressed the 
statement at the end of the first paragraph. How did my best circuit come 
to be? That's a long story. Here it is. 

The Postpartum Blues 

Towards the end of 1991 I was in a mt. I had finished a large high-speed 
amplifier project in August. It had required a year of constant, intense, and 
sometimes ferocious effort right up to its conclusion. Then it was over, 
cind I suddenly had nothing to do. I have found myself abruptly discon- 
nected from an absorbing task before, and the result is always the same. 
I go into this funky kind of rut, and wonder if I'll ever find anything else 
interesting to do, and if I'm even capable of doing anything anymore. 



Portions of this text have appeared in the January 6, 1994 issue of EDN magazine and publica- 
tions of Linear Technology Corporation. They are used here with permission. 



139 



Tripping the Light Fantastic 



I've been dating me a long time, so this state of mind doesn't promote 
quite the panic and urgency it used to. The treatment is always the same. 
Keep busy with mundane chores at work, read, cruise electronic junk 
stores, fix things and, in general, look available so that some interesting 
problem might ask me to dance. During this time I can do some of the 
stuff I completely let go while I was imrnersed in whatever problem 
owned me. The treatment always seems to work, and usually takes a pe- 
riod of months. In this case it took exactly three. 

What's a Backlight? 

Around Christmas my boss. Bob Dobkin, asked me if I ever thought 
about the liquid crystal display (LCD) backlights used in portable com- 
puters. I had to admit I didn't know what a backlight was. He explained 
that LCD displays require an illumination source to make the display 
readable, and that this source consumed about half the power in the ma- 
chine. Additionally, the light source, a form of fluorescent lamp, requires 
high-voltage, high-frequency AC drive. Bob was wondering how this was 
done, with what efficiency, and if we couldn't come up with a better way 
and peddle it. The thing sounded remotely interesting. I enjoy transducer 
work, and that's what a light bulb is. I thought it nfiight be useful to get 
my hands on some computers and take a look at the backlights. Then I 
went off to return some phone calls, attend to other housekeeping type 
items, and, basically, maintain my funk. 

A CafI from Some Guy Itei^ 

Three days later the phone rang. The caller, a guy named Steve Young 
from Apple Computer, had seen a cartoon (Figure U-1) I stuck on the 
back page of an application note in 1989. Since the cartoon invited calls, 
he was doing just that. Steve outlined several classes of switching power 
supply problems he was interested in. The application was portable com- 
puters, and a more efficient backlight circuit was a priority. Dobkin's 
interest in backlights suddenly sounded a lot less academic. 

This guy seemed like a fairly senior type, and Apple was obviously a 
prominent computer company. Also, he was enthusiastic, seemed easy to 
work with and quite knowledgeable. This potential customer also knew 
what he wanted, and was willing to put a lot of front end thinking and 
time in to get it. It was clear he wasn't interested in a quick fix; he wanted 
true, "end-to-end" system cniented thinking. 

What a customer! He knew what he wanted. He was open and anxious 
to work, had time and money, and was willing to sweat to get better solu- 
tions. On top of all that, Apple was a large and successful company with 
excellent engineering resources. I set up a meeting to introduce him to 
Dobkin and, hopefully, get something started. 



140 



JtmWHHams 



Application Note 35 




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r\rj Linear Technology Corporation inf= An 

t630l<teCartiy Bl«di, Milf»tas,GA 95035^ • (408}432-1900 JL/ UJSQ^ 

FAX:(408)434-O607 ♦TELEX: 49^3977 © linear TECHNOLowcoRi^iwaiiJNtiw 

This invitation appeared in a 1989 application note. Some guy named Steve Young from Appfe Gomputi^ todk 
me up on it. (Reproduced with permission of Linear Technology Corporation) 

141 



Tripping the Light Fantastic 



The meeting went well, things got defined, and I took the backlight 
problem. I still wasn't enthralled with backlights, but here was an almost 
ideal customer falling in through the roof so there really wasn't any 
choice. 

Steve introduced me to Paul Donovan, who would become my primary 
Apple contact. Donovan outlined the ideal backlight. It should have the 
highest possible efficiency, that is, the highest possible display luminos- 
ity with the lowest possible battery drain. Lamp intensity should be 
smoothly and continuously variable over a wide range with no hysteresis, 
or **pop-on,** and should not be affected by supply voltage changes. RF 
emissions should meet FCC and system requirements. Finally, parts 
count and board space should be minimal. There was a board height re- 
quirement of .25". 



Getting Staitech-TheLuctdtte Approach taUarr^ 



Figure 11-2. 
Architecture of a 
typfcallamp driver 
board. There is no 
form of feedback 
from the lamp. 



I got started by getting a bunch of portable computers and taking them 
apart. I must admit that the Luddite in me enjoyed throwing away most 
of the computers while saving only their display sections. One thing I 
immediately noticed was that almost all of them utilised a purchased, 
board-level solution to backlight driving. Almost no one actually built the 
function. The circuits invariably took the form of an adjustable output 
step-down switching regulator driving a high voltage DC- AG inverter 
(Figure 11-2). The AC high- voltage output was often about 50kH^, and 
approximately sinusoidal. The circuits seemed to operate on the assump- 
tion that a constant voltage input to the DC- AC inverter would produce a 
fixed, high voltage output. This fixed output would, in turn, produce con- 
stant lamp light emission. The ballast capaeitor's function was not en- 
tirely clear, but I suspected it was related to lamp characteristics. There 
was no form of feedback from the lamp to the drive circuitry. 

Was there something magic about the 50kHz frequency? To see, I built 
up a variable-frequency high voltage generator (Figure 11-3) and drove 
the displays. I varied frequency while comparing electrical drive power 



POWER 
SWITCH 



BAllA$r 

CAPACITOR 



T 



REGULATOR 



FEEDBACK 



DC/AC 
HIGH VOLTAGE 
CONVERTER 



LAMP 



142 



Jim Williams 



UK0 LS-52 
AUDIO 
TRANSFORMER 



BALLAST 
CAPACITOR 




HP-300CD 
SINE WAVE 
OSCILLATOR 



to optical emission. Lamp conversion efficiency seemed independent of 
frequency over a fairly wide range. I did* however, notice that higher 
frequencies tended to introduce losses in the wiring running to the lamp. 
These losses occurred at all frequencies, but became pronounced above 
about lOOkHz or so. Deliberately introducing parasitic capacitances from 
the wiring or lamp to ground substantially increased the losses. The les- 
son was clear. The lamp wiring was an inherent and parasitic part of the 
circuit, and any stray capacitive path was similarly parasitic. 

Armed with this information I returned to the computer displays. I 
modified things so that the wire length between the inverter board and 
display was minimized. I also removed the metal display housing in 
the lamp area. The result was a measurable decrease in inverter drive 
power for a given display intensity. In two machines the improvement 
approached 20%! My modifications weren't very practical from a me- 
chanical integrity viewpoint, but that wasn't relevant. Why hadn*t these 
computers been originally designed to take advantage of this **free" effi- 
ciency gain? 



Rgure11-3, 

Variable frequency 
high-voltage test 
setup for evaluating 
lamp frequency 
sensitivity. 



Playing around with Light Bulbs 

I removed lamps from the displays. They all appeared to have been in- 
stalled by the display vendor, as opposed to being selected and purchased 
by the computer manufacturer. Even more interesting was that I found 
identical backlight boards in different computers driving different types 
of lamps. There didn't seem to be any board changes made to accommo- 
date the various lamps. Now, I turned my attention to the lamps. 

The lamps seemed to be pretty complex and wild animals. I noticed 
that many of them took noticeable time to arrive at maximum intensity. 
Some types seemed to emit more light than others for a given input 
power. Still others had a wider dynamic range of intensities than the rest, 
although all had a seemingly narrow range of intensity control. Most 
striking was that every lamp's emissivity varied with ambient tempera- 



Tripping the Light Fantastic 



ture. Experimenting with a hair dryer, a can of "cold spray" and a pho- 
tometer, I found that each lamp seemed to have an optimum operating 
temperature range. Excursions above or below this region caused emit- 
tance to fall. 

I put a lamp into a reassembled display. With the display warmed up in 
a 25 °C environment I was able to increase light output by sUghtly venti- 
lating the lamp enclosure. This increased steady-state therm^ tosses, 
allowing the lamp to run in its optimum temperature range. I also saw 
screen illumination shifts due to the distance between the light entry point 
at the display edge and the lamp. There seemed to be some optimmti dis- 
tance between the lamp and the entry point. Simply coupling the lamp as 
closely as possible did not provide the best results. Similarly, the metallic 
reflective foil used to concentrate the lamp's output seemed to be sensi- 
tive to placement. Additionally, there was clearly a trade-off between 
benefits from the foil's optical reflection and its absorption of high volt- 
age field energy. Removing the foil decreased input energy for a given 
lamp emission level. I could watch input power rise as I slipped tbe foil 
back along the lamp's length. In some cases, with the foil fully replaced, I 
could draw sparks from it with my finger! 

I also assembled lamps, displays, and inverter boards in various un- 
original combinations. In some cases I was able to increase light output, 
at lower input power drain, over the original "as shipped" configuration. 

Grandpa Would Have Liked It 

I tried a lot of similarly simple experiments and slowly developed a 
growing suspicion that nobody, at least in my sample of coniputers, was 
making any serious attempt at optimizing (or they did not know how to 
optimize) the backlight. It appeared that rnost people niaking lareq>s were 
simply filling tubes up with gas and shipping them. Display manufactur- 
ers were dropping these lamps into displays and shipping them. Com- 
puter vendors bought some "backlight power supply" board, wired it up 
to the display, took whatever electrical and optical efficiency they got, 
and shipped the computer. 

If I allowed this conclusion, several things became clear. Development 
of an efficient backlight required an interdisciplinary approach to address 
a complex problem. There was worthwhile work to be done. I could con- 
tribute to the electronic portion, and perhaps the thermal design^ but the 
optical engineering was beyond me. It was not, however, beyond Apple's 
resources. Apple had some very good optical types. Working together, it 
seemed we had a chance to build a better backlight with its attendant 
display quality and battery life advantages. Apple would get a more 
saleable product and my company would develop a valued customer. And, 
because the whole thing was beginning to get interesting, I could get out 
of my rut. The business school types would call this "synergistic" or 
"win-win." Other people who "do lunch" a lot on company money would 



144 



call it "strategic partnering." My grandfather would have called it "such a 
deal." 

Goals for the backlight began to emerge. For best overall efficiency, 
the display enclosure, optical design, lamp, and electronics had to be 
simultaneously considered. My job was the electronics, although I met 
regularfy with Paul Donovan, who was working on the other issues. In 
particular, I was actively involved in setting lamp specifications and eval- 
uating lamp vendors. 

The electronics should obviously be as efficient as possible. The cir- 
cuit should be physically conq)act, have a low parts count, and assemble 
easily. It should have a wide, continuous dimming range with no hystere- 
sis or "pop-on," and should meet all RF and system emisston require- 
ments FinaUy, it must regulate lamp intensity against wide power supply 
shifts, such as when the computer's AC adapter is plugged in. 

He^fr^Dt^y Circuits 

Where, I wondered, had I seen circuitry which contained any or all of 
these characteristics? Nowhere. But, one place to start looking was oscil- 
loscopes. Although oscilloscope circuits do not accompKsh what I needed 
to do, oscilloscope designers use high frequency sine wave conversion to 
generate the high voltage CRT supply. This technique minimizes noise 
and reduces transformer and capacitor size. Additionally, by doing the 
conversion at the CRT, long high voltage runs from the main power sup- 
ply are eliminated. 

I looked at the schematic of the high voltage converter in a Tektronix 
547 (Figure 1 1-4). The manual's explanation (Figure 1 1-5) says the 
capacitor (C808) and transformer primary form a resonant tank circuit. 
More subtly, the "transformer primary" also includes the complex imped- 
ance reflected back from the secondary and its load. But that's a detail for 
this circuit and for now. A CRT is a relatively linear and benign load. 
The backlight's loading characteristics would have to be evaluated and 
matched to the circuit. 

This CRT circuit could not be used to drive a fluorescent backlight 
tube in a laptop computer. For one reason, this circuit is not very efficient. 
It does not have to be. A 547 pulls over 500 watts, so efficiency in this 
circuit was not a big priority. Latter versions of this configuration were 
transistorized (Figure 1 1-6, Tektronix 453), but used basically the same 
architecture. In both circuits the resonating technique is employed, and a 
feedback loop enforces voltage regulation. For another reason, the CRT 
requires the high voltage to be rectified to DC. The backlight requires AC, 
eliminating the rectifier and filter. And, the CRT circuit had no feedback. 
Sonn^e forna of feedback for the fluorescent lamp seemed desirable. 

The jewel in the CRT circuit, however, was the resonating technique 
used to create the sine wave. The transformer does double duty. It helps 
create the sme wave while simultaneously generating the high voltage. 



Tripping the Light Fantastic 




<^ POWtR SUPPLY e HEAT£.R WIRING DIAC>. 

<^ >' &WLbP ALNtRATOR 

HORiZOMTAL tM&PUAY SWITCH 
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SEE PARTS UST FQ<t EMUtt 
VALUES X'hSi SfMAl NUMSCa 
RANGES OF >AltTS MMMEO 
WITH BlUE OUTUNE. 

SEE PARTS LIST FOR 
SCMICOKlbUCTOO TYPES 



TYPt 547 OSCILLOSCOPt 



146 



Jkn Williams 



fir 



UMBt.M«<UM« 




_ CRT CIRCUIT <A> 

R8yre11-4. 

CRT supply used in Tektronix 547. C808 resonates wfth transformer, creating sine wave drive. (Pigure repro- 
duced with permission of Tektronix, Inc.) 



147 



Tripping the Light Fantastic 



Figure 11-5. 
Tektronix 547 
mamial explains 
resonant operation. 
(Figure reproduced 
with permission of 
TeWronix, Inc.) 



Crt Circuit 

The crt circuit (see Crt schematic) includes the crt, the 
high-voltage power supply, and the controls necessary to 
focus and orient the display. The crt (Tektronix Type 
T5470.31-2) is an aluminized, 5-inch, flat-faced, glass crt with 
a helical post-accelerator and electrostatic focus and de- 
flection. The cft circuit provides connections for externally 
modulating the crt cathode. The high-voltage power supply 
is composed of a dc-tp-50-kc power converter, a voltage- 
regulator circuit, and three high-voltage outputs. Front- 
panel controls in the crt circuit adjust the trace rotation 
(screwdriver adjustment), intensity, focus, and astigmatism. 
Internal controls adjust the geometry and high-voltage out- 
put level. 

High-Voltage Power Supply. The high-voltage power sup- 
ply is a dc-to-ac converter operating at approximately 50 kc 
with the transformer providing three high-voltage outputs. 
The use of a 50-kc input to the high-voltage transformer 
permits the size of the transformer and filter components 
to be kept small. A modified Hartley oscillator converts 
dc from the -f 325-voIt unregulated supply to the 50-kc Input 
required by high-voltage transformer T801. C808 and the 
primary of T801 form the oscillator resonant tank circuit, 
No provisions are made for precise tuning of the oscillator 
tank since the exact frequency of oscillation is not important. 

Voltage Regulation. Voltage regulation of the high-voltage 
outputs is accomplished by regulating the amplitude of 
oscillations in the Hartley oscillator. The — 1850«voft output 
is referenced to the -f 350-volt regulated supply through a 
voltage divider composed of R841, R842, R843, R845, R846, 
R847, Re53, and variable resistors R840 and R846. Through 
a tap on the voltage divider, the regulator circuit samples 
the — 1850-volt output of the supply, amplifies any errors 
and uses the amplified error voltage to adjust the screen 
voltage of Hartley oscillator V800. If the —1850-volt output 
changes, the change is detected at the grid of V814B. The 
detected error is amplified by V814B and V814A. The error 
signal at the plate of V8I4A is direct coupled to the screen 
of V800 by making the plate-load resistor of V814A serve as 



How could I combine this circuit's desirable resonating characteristics 
with other techniques to meet the baeklight's requirements? One key was 
a simple, more efficient transformer drive. I knew just where to find it. 

In December 1954 the paper "Transistors as On-Off Switches in 
Saturable-Core Circuits" appeared in Electrical Manufacturing. George 
H. Royer, one of the authors, described a "d-c to a-c converter'' as part 
of this paper. Using Westinghouse 2N74 transistors, Royer reported 
90% efficiency for his circuit. The operation of Royer's circuit is well 
described in this paper. The Royer converter was widely adopted, and 
used in designs from watts to kilowatts. It is still the basis for a wide 
variety of power conversion. 



148 



Rover's circuit is not an LC resonant type. The transformer is the sole 
energy storage element and the output is a square wave. Figure 1 1-7 is a 
conceptual schematic of a typical converter. The input is applied to a self- 
oscillating configuration composed of transistors, a transformer, and a 
biasing network. The transistors conduct out of phase switching (Figure 
11-8: Traces A and C are Ql's collector and base, while Traces B and D 
are Ql's collector and base) each time the transformer saturates. Trans- 
former saturation causes a quickly rising, high current to flow (Trace E). 

This current spike, picked up by the base drive winding, switches the 
transistors. This phase opposed switching causes the transistors to ex- 
change states. Current abruptly drops in the formerly conducting tran- 
sistor and then slowly rises in the newly conducting transistor until 
saturation again forces switching. This alternating operation sets tran- 
sistor duty cycle at 50%. 

The photograph in Figure 1 1-9 is a time and amplitude expansion of 
Figure 1 1-8's Traces B and E. It clearly shows the relationship between 
transformer cuitent (Trace B, Figure 1 1-9) and transistor collector volt- 
age (Trace A, Figure 1 1-9).* 

The Royer has many desirable elements which are applicable to back- 
light driving. Transformer size is small because core utilization is effi- 
cient. Parts count is low, the circuit self-oscillates, it is efficient, and 
output power may be varied over a wide range. The inherent nature of 
operation produces a square wave output, which is not permissible for 
backlight driving. 

Adding a capacitor to the primary drive (Figure 11-1 0) should have the 
same resonating elfect as in the Tektronix CRT circuits. The beauty of this 
configuration is its utter simplicity and high efficiency. As loading (e.g., 
lamp intensity) is varied the reflected secondary impedance changes, caus- 
ing some frequency shift, but efficiency remains high. 

The Royer*s output power is controllable by varying the primary drive 
current. Figure 1 1-1 1 shows a way to investigate this. This circuit works 
well, except that the transistor current sink operates in its linear region, 
wasting power. Figure 1 1-12 converts the current sink to switch mode 
<jperation, maintaining high efficiency. This is obviously advantageous to 
the user, but also a good deal for my employer. I had spent the last six 
months playing with light bulbs, reminiscing over old oscilloscope cir- 
cuits, taking arcane thermal rneasurements, and similar dalliances. All the 
while faithfully collecting my employer's money. Finally, I had found a 
place to actu£dly sell something we made. Linear Technology (my em- 
ployer) builds a switching regulator called the LTl 172. Its features include 
a high power open collector switch, trimmed reference, low quiescent 
ditmif, and sbutdown cap^ility. Additionally, it is available in an 8 pin 
surface-mount package, a must for board space considerations. It was also 
an ideal candjdale for the circuit's current sink portion. 



I . The boUQin traces in both photographs are not germane and are not referenced in the discussion. 



Tripping the Light Fantastic 



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150 



Jim Williams 



- S.foM. 



UNaLANK.tN& GATE. 
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CRT CIRCUIT <^ 
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Figure 11-6. 

Later model Tektronix 453 is transistorized version of 547's resortant approacli. (Figure reproduced with permis- 
sion of Tektronix, Inc.) 



151 



Tripping the Light Fantastic 



Figure 11-7. 

Conceptual classic 
Royer converter, 
Transfomrier ap- 
proaching satura- 
tion causes 
switching. 




Of Rafts and Paddles 

At abK>ut this stage I sat back and stared at the wall. There conies a time in 
every project where you have to gamble. At some point the analytics and 
theorizing must stop and you have to conmiit to an approach and start 
actuaUy doing something. This is often painfiil, because you never really 
have enough information and preparation to be confidently decisive. There 
are never any answers, only choices. But there comes this time when your 
gut tells you to put down the pencil and pick up the soldering iron. 

Physicist Richard Feynman said, **If you're not confused when you 
start, youVe not doing it right " Somebody else, I think it was an artist, 
said, "Inspiration comes while working " Wow, are they right. With cir- 
cuits, as in life, never wait for your ship to come in. Build a raft and start 
paddling. 



Rgure11*a. 

Waveforms for the 
classic Royer 
circuit. 




Jim Williams 



A = 10V/DIV 




Figure 11-9. 

Detail of transistor 
switching. Turn-off 
(Trace A) occurs 
just as transformer 
heads into satura- 
tion (Trace B). 



HORIZ = 500ns/DIV 



Everything was still pretty fiizzy, but I had learned a few things, A 
practical, highly efficient LCD backlight design is a classic study of com- 
promise in a transduced electronic system. Every aspect of the design is 
interrelated, and the physical embodiment is an integral part of the elec- 
trical circuit. The choice and location of the lamp, wires, display housing, 
and other items have a major effect on electrical characteristics. The 
greatest care in every detail is required to achieve a practical, high effi- 
ciency LCD backlight. Getting the lamp to light is just the beginning! 

A good place to start was to reconsider the lamps. These "Cold 
Cathode Fluorescent Lamps'* (CCFL) provide the highest available effi- 
ciency for converting electrical energy to light. Unfortimately, they are 
optically and electrically highly nonlinear devices. 




Figure 11-10, 

Adding the resonat- 
ing capacitor to the 
Royer 



Tr^n^ng the Light Fantastic 




Cold Cathode Fluorescent Lamps (CCFLs) 

Any discussion of CGFL power supplies must consider lat^ characteris- 
tics. These lamps are complex transducers, with many variables affecting 
their ability to convert electrical current to light. Factors influencing con- 
version efficiency include the lamp's current, temperature, drive wave- 
form characteristics, length, width, gas constituents, and the proximity to 
nearby conductors. 

These and other factors are interdependent, resulting in a complex 
overall response. Figures 11-13 through 11-16 show some typical char- 
acteristics. A review of these curves hints at the difficulty in predicting 
lamp behavior as operating conditions vary. The lamp's current and tem- 
perature are clearly critical to emSssion, although electrical efficiency 
may not necessarily correspond to the best optical efficiency point. 
Because of this, both electrical and photometric evaluation of a circuit is 
often required. It is possible, for example, to construct a CCFL circuit 
with 94% electrical efficiency which produces less light output than an 
approach with 80% electrical efficiency (see Appendix C, "A Lot of Cut- 
off Ears and No Van Goghs — Some Not-So-Great Ideas"). Similarly, the 
performance of a very well matched lamp-circuit combination can be 



154 



JimWilliains 




VVSr- 




POWER 
SWITCHING 



BASE BIASING 
AND DRIVE 




VlN 





SWITCH MODE 




>— 


REGULATOR 





i' 



severely degraded by a lossy display enclosure or excessive high voltage 
wire lengths. Display enclosures with too much conducting material near 
the lamp have huge losses due to capacitive coupling. A poorly designed 
display enclosure can easily degrade efficiency by 20%. High voltage 
wire runs typically cause 1% loss per inch of wire. 



Figure 11-12. 

Switched mode 
current sink re- 
stores eff ictency. 




Tripling the Light Fantastic 



Figure 11-14. 

Ambient tempera- 
ture effects on 
emissivlty of a 
typical 5mA lamp. 
Lamp and enclo- 
sure must come to 
thermal steady 
state before 
measurements 
are made. 




-10 0 10 20 30 40 50 80 70 
AMBIENT TEMPERATURE ("C) 



CCFL Lo»j Characteristics 

These lamps are a difficult load to drive, particularly for a switching regu- 
lator. They have a "negative resistance" characteristic; the starting voltage 
is significantly higher than the operating voltage. Typically, the start volt- 
age is about lOOOV, although higher and lower voltage lamps are com- 
mon. Operating voltage is usually 300V to 400V, although other lamps 
may require different potentials. The lamps will operate from DC, but 
migration effects within the lamp will quickly damage it. As such, the 
waveform must be AC. No DC content should be present. 

Figure 1 1-1 7 A shows an AC driven lamp's characteristics on a curve 
tracer. The negative resistance induced "snapback" is apparent. In Figure 
1 1^17B, another lamp, acting against the curve tracer's drive, produces 
oscillation. These tendencies, combined with the frequency comp^a- 
tion problems associated with switching regulators, can cause severe loop 
instabilities, particularly on start-up. Once the lamp is in its operating 
region it assumes a linear load characteristic, easing stability criteria. 
Lamp operating frequencies are typically 20kHz to lOOkHz and a sine- 




156 



Jim Williams 



1000 
800 

I 

i 

S 400 

200 

































1 . 



Figure 11-16. 

Running voltage vs. 
lamp length at two 
temperatures. 
Start-up voltages 
are usually 50% to 
200% higher over 
temperature. 



100 200 
TUBE UENGTH (mm) 



300 



like waveform is preferred. The sine drive's low harmonic content mini- 
mizes RF emissions, which could cause interference and efficiency 
degradation, A further benefit of the continuous sine drive is its low crest 
factor and controlled risetimes, which are easily handled by the CCFL. 
CCFUs RMS current-to-light output efficiency is degraded by high crest 
factor drive waveforms.^ 

CCFL Power Supply Circuits 

Figure 1 1-I8*s circuit meets CCFL drive requirements. Efficiency is 
88% with an input voltage range of 4.5V to 20V. This efficiency figure 
will be degraded by about 3% if the LTl 172 Vy^ pin is powered from the 
sante supply as the main circuit Vn^ terminal. Lamp intensity is continu- 
ously and smoothly variable from zero to full intensity. When power is 



Figure 11-17. 

Negative resistance 
characteristic for 
two CCFL lamps, 
"Snap-back" is 
readily apparent, 
causing oscillation 
in 11-17B, These 
characteristics 
complicate power 
supply design. 





H0RIZ = 200V/DIV 

17A 



HORIZ = 200V/DIV 

17B 



2. See Appendix C, "A Loi of Cut-off Ears and No Van Goghs — Some Not-So-Grcat Ideas." 



157 



Tripping the Light Fantastic 



Figure 11-18. 

An 88% efficiency 
cold cathode fluo- 
rescent lamp 
(CCFL) power 
supply. 



200ii 

TESTONIY 

(SEE TEXT) 




C1 = MUST BE A LOW LOSS CAPACITOR. 
METALIZED POLYCARB 

WIMA FKP20R MKP-20 (GERMAN) RECOMMENDED 
L1 = SUMIDA 6345-020 OR COILTRONICS CTX11Q092-1 

PIN NUMBERS SHOWN FOR COILTRONICS UNIT 
L2 = COILTRONICS CTX300-4 
01 , Q2 - ZETEX ZTX849 OR ROHM 2SC5001 
•«1%flLMR£SfST0R 

mm sirismmi COMPONENTS 



COILTRONICS (305) 781-8900. SUMIDA (708) 956-0666 



applied the LTl 172 switching regulator's feedback pin is l^elow the de- 
vice's internal 1 ,2V reference, causing full duty cycle modulation ai the 
pin (Trace A, Figure 11-19). L2 conducts current (Trace B) which 
flows from Li's center tap, through the transistors, into L2. L2's current 
is deposited in switched fashion to ground by the regulator's action. 

LI and the transistors comprise a current driven Royer class converter 
which oscUlates at a frequency primarily set by Li's characteristics (in- 
cluding its load) and the .033^F capacitor. LTl 172 driven L2 sets the mag- 
nitude of the Q1-Q2 tail current, and hence Li's drive level. The 1N5818 
diode maintains L2's current flow when the LTl 172 is off. The LTl 172's 
lOOkHz clock rate is asynchronous with respect to the push-pull con- 
verter's (60kHz) rate, accounting for Trace B's waveform thickening. 



158 



Jim WiiBams 




AANDBH0RIZ-4^s/DlV 
C THRU F HORIZ = 20^s/DIV 
TRIGGERS FULLY INDEPENDENT 



reseent lamp power 
suppiy.>Jot8inde- 
pehderrttrigg^ing 
on Traces A and B, 
and C through R 



The .033^iF capacitor combines with Li's characteristics to produce 
sine wave voltage drive at the Ql and Q2 collectors (Traces C and D, re- 
spectively). LI furnishes voltage step-up, and about 1400V p-p appears at 
its secondary (Trace E). Current flows through the 15pF capacitor into the 
lamp. On negative waveform cycles the lamp's current is steered to ground 
via DL Positive waveform cycles are directed, via D2, to the ground re- 
ferred 562fl-50k potentiometer chain. The positive half-sine appearing 
across the resistors (Trace F) represents M the lamp current. This signal is 
filtered by the lOk-l^F pair and presented to the LTl 172's feedback pin. 
This connection closes a control loop which regulates lamp current. The 
2\xF capacitor at the LTl 172's Vc pin provides stable loop compensation. 
The loop forces the LTl 172 to switch-mode modulate L2*s average current 
to whatever value is required to maintain a constant current in the lamp. 
The constant current's value, and hence lamp intensity, may be varied with 
the potentiometer. The constant current drive allows fiiU 0%-t(K)% in- 
tensity control with no lamp dead zones or "pop-on*' at low intensities* 
Additionally, lamp life is enhanced because current cannot increase as 
the lamp ages. This constant current feedback approach contrasts with 
the open loop, voltage type drive used by other approaches. It greatly 
improves control over the lamp under all conditions. 

This circuit's 0.1% line regulation is notably better than some other 
approaches. This tight regulation prevents lamp intensity variation when 
abrupt line changes occur. This typically happens when battery powered 
apparatus is cormected to an AC powered charger. The circuit's excellent 
line regulation derives from the fact that Li's drive waveform never 
changes shape as input voltage varies. This characteristic permits the 
simple 10k£l-ijiF RC to produce a consistent response. The RC averag- 
ing characteristic has serious error compared to a tme RMS conversion, 
but the error is constant and ^'disappears" in the 56212 shunt's value. The 
base drive resistor's value (nominally IkQ) should be selected to provide 



Tripping the Light Fantastic 

full saturation without inducing base overdrive or beta starvation. A 
procedure for doing this is described in the following section, '^General 
Measuren^nt and C^timization Considerations " 

Figure 1 1-20's circuit is similar, but uses a transformer with lower cop- 
per and core losses to increase efficiency to 91 %. The trade-off is siightiy 
larger transformer size. Value shifts in CI, L2, and the base drive msistor 
reflect different transformer characteristics. This circuit also features shut- 
down via Q3 and a DC or pulse width controlled dimming input. Figure 
1 1-21, directly derived from Figure 1 1-20, produces 10mA output to 
drive color LCDs at 92% efficiency. The slight efficiency improvement 
comes from a reduction in LTl 172 "hou^keeping" current as a percentage 



A 91% efficient 
CCFL supply for 
5fn A loads features 
shutdown and 
dtrTKnIng inputs. 



200D 

TESTONLY 
(3KTEXT) 












E1 






LT1172 






E2 






GND 





SHUTDOWN DIMMING INPUT 
C1=WIMAMKP-20 (SEE TEXT) 

L1 =COlLTRONICSCTX150-4 
Q1, Q2 = ZETEX ZTX849 OR ROHM 2SC5001 

T1 - COILTRONICS CTX1 10600-1 OR SUMIDA EPS-207 
PIN NUMBERS SHOWN FOR COILTRONICS UNIT 
* = 1% FILM RESISTOR 

DO KOT SUBSTITUTE COMPONENTS 



COILTRONICS (305) 781-8900, SUMIDA (708) 956-0666 



160 



Jim Williams 



of total current drain. Value changes in components are the result of higher 
power operation. The most significant change involves driving two tubes. 
Accommodating two lamps involves separate ballast capacitors but circuit 
operation is similar. Two lamp designs reflect slightly different loading 
back through the transformer's primary. C2 usually ends up in the lOpF to 
47pF range. Note that C2A and B appear with their lamp loads in parallel 
across the transformer's secondary. As such, C2's value is often smaller 
than in a single tube circuit using the same type lamp. Ideally the trans- 
former's secondary current splits evenly between the C2-lamp branches, 
with the total load current being regulated. In practice, differences between 
C2A and B and differences in lamps and lamp wiring layout preclude a 
perfect current split. Practically, these differences are small, and the 




Figure 11-21. 
A 92% efficient 
CCFL supply for 
10mA loads fea- 
tures shutdown 
and dimming in- 
puts. Two lamps 
are typical of color 
displays. 











E1 






LT1172 






E2 


Vfb 




GND 





SHUTDOWN DIMMING INPUT 
CT---WIMAMKP-20 (SEE TEXT) 

L1-COIITRONICSCTX150-4 
01 , Q2 ZETEX ZTX849 OR ROHM 2SC5001 

T1 = COILTRONICS CTX110600-r OR SUMIDA EPS-207 
PIN NUMBERS SHOWN FOR COlLTRONICS UNIT 

FILM RESISTOR 
DO NOT SUBSTITUTE COMPONENTS 



COlLTRONICS (305) 781-8900, SUMIDA (708) 956-0666 



161 



Tripping the Light Fantastic 



lamps appear to emit equal Mnounts of light. Layout and lamp matching 
can influence C2's value. Some techniques for dealing with these issues 
appear in the section "Layout Issues." 

General Measinsmmt and Op^zation 
Considerations 

Several points should be kept in mind when observing operation of these 
circuits. Li's high voltage secondary can only be monitored with a wide- 
band, high voltage probe fiilly specified for this type of measurement. The 
vast majority of oscilloscope probes will break down and fail if used for 
this measurement Tektronix probe types P6007 and P6009 (acceptable) or 
types P601 3A and P601 5 (preferred) must be used to read LI 's output. 

Another consideration involves observing waveforms. The LTl 1 72's 
switching frequency is completely asynchronous from the Q1-Q2 Royer 
converter's switching. As such, most oscilloscopes cannot simultaneously 
trigger and display all the circuit's waveforms. Figure 1 1-19 was obtained 
using a dual beam oscilloscope (Tektronix 556). LTl 172 related Traces A 
and B are triggered on one beam, while the remaining traces are triggered 
on the other beam. Single beam instmments with alternate sweep and 
trigger switching (e.g., Tektronix 547) can also be used, but are less ver- 
satile and restricted to four traces. 

Obtaining and verifying high efficiency^ requires some amount of dili- 
gence. The optimum efficiency values given for CI and C2 are typical, and 
will vary for specific types of lamps. An important realization is that the 
term "lamp" includes the total load seen by the transformer's secondary. 
This load, reflected back to the primary, sets transformer input impedance. 
The transformer's input impedance forms an integral part of the LC tank 
that iH'oduces the high voltage drive. Because of this, circuit efficiency 
must be optimized with the wiring, display housing and physical layout 
arranged exactly the same way they will be built in production. Deviations 
from this procedure will result in lower efficiency than might otherwise be 
possible. In practice, a "first cut" efficiency optimization with "best guess" 
lead lengths and the intended lamp in its display housing usually produces 
results within 5% of the achievable figure. Final values for CI and C2 may 
be established when the physical layout to be used in production has been 
decided on. CI sets the circuit's resonance point, which varies to some 



3. The terra **efficiency*' as used here applies to electrical efficiency. In fact, the ultiinate concern 
centers around the efficient conversion of power supply energy into light. Unfortunately, lamp 
types show considerable deviation in their current-to-light conversion efficiency Similarly, the 
emitted light for a given current varies over the life and history of any particular Iw i \{) A . . uch, 
this publication treats "efficiency" on an electrical basis; the ratio of power removed from the 
primary supply to the power delivered to the lamp. When a lamp has been selected, the ratio 
of primary supply power to lamp-emitted light energy may be tneasured with the aid of a pho- 
tometer. This is covered in Appendix B, "Photometric Measurenoents." See also Appendix D, 
"Perspectives on Efficiency." 



162 



extent with the lamp's characteristics. C2 ballasts the lamp, effectively 
buffering its negative resistance characteristic. Small values of C2 provide 
the most load isolation, but require relatively large transformer output 
voltage for loop closure. Large C2 values minimize transformer output 
voltage, but degrade load buffering. Also, Cl's "best" value is somewhat 
dependent on the lamp type used. Both CI and C2 must be selected for 
given lamp types. Some interaction occurs, but generalized guidelines are 
possible. Typical values for CI are 0.01|iF to .15(iF. C2 usually ends up in 
the 1 OpF to 47pF range. CI must be a low-loss capacitor and substitution 
of the recommended devices is not recommended. A poor quality dielec- 
tric for CI can easily degrade efficiency by 10%. CI and C2 are selected 
by trying different values for each and iterating towards best efficiency. 
During this procedure, ensure that loop closure is maintained by monitor- 
ing the LTl 172's feedback pin, which should be at 1 .23V. Several trials 
usually produce the optimum CI and C2 values. Note that the highest 
efficiencies are not necessarily associated with the most esthetically pleas- 
ing waveshapes, particularly at Ql, Q2, and the output. 

Other issues influencing efficiency include lamp wire length and en- 
ergy leakage from the lamp. The high voltage side of the lamp should 
have the smallest practical lead length. Excessive length results in radia- 
tive losses, which can easily reach 3% for a 3 inch wire. Similarly, no 
metal should contact or be in close proximity to the lamp. This prevents 
energy leakage, which can exceed 10% ^ 

It is worth noting that a custom designed lamp affords the best possi- 
ble results. A jointly tailored lamp-circuit combination permits precise 
optimization of circuit operation, yielding highest efficiency. 

Special attention should be given to the layout of the circuit board, 
since high voltage is generated at the output. The output coupling capaci- 
tor must be carefully located to minimize leakage paths on the circuit 
board. A slot in the board will further minimize leakage. Such leakage 
can permit current flow outside the feedback loop, wasting power. In the 
worst case, long term contamination build-up can increase leakage inside 
the loop, resulting in starved lamp drive or destructive arcing. It is good 
practice for minimization of leakage to break the silk screen line which 
outlines transformer Tl . This prevents leakage from the high voltage 
secondary to the primary. Another technique for minimizing leakage is to 
evaluate and specify the silk screen ink for its ability to withstand high 
voltages. 



4. A very simple experiinent quite nicely demonstrates the effects of energy leakage. Grasping the 
lamp at its low^ voltage end (low field intensity) with thumb and lorefin^ piodQoes no 
ch^ge in circuit input current Sliding the thumb^loiellnger combin^^cnt towaiids tlie tugh- 
Voltage (M^r^d intensity) lainp end piKKluces progressively ^^rippiKt currents. Don't 
touch the high-vc^^ lead or you noay receive an elecoical shocks Repeat: I>o not touch the 
high' voltage lead or you may receive an electrical shock. 



Tdpi»iig the Light Fantastic 

Eff icieiu;y Measui^nie^^ 



Once these procedures have been followed efficiency can be nieasured. 
Efficiency may be measured by determining lamp current and voltage. 
Measuring current involves measuring RMS voltage across a temporarily 
inserted 200Q .1 % resistor in the ground lead of the negative cun ent 
steering diode. The lamp current is 

ERMS 
Ilamp = X 2 

The x2 factor is necessitated because the diode steering dumps the cur- 
rent to ground on negative cycles. The 200Q value allows the RMS meter 
to read with a scale factor numerically identical to the total current. Once 
this measurement is complete, the 200fl resistor may be deleted and the 
negative current steering diode again returned directly to ground. Lamp 
RMS voltage is measured at the lamp with a properly compensated high 
voltage probe. MuUiplying these two results gives power in watts, which 
may be compared to the DC input supply E x I product. In practice^ the 
lamp's current and voltage contain small out of phase components but 
their error contribution is negligible. 

Both the current and voltage measurements require a wideband true 
RMS voltmeter. The meter must employ a thermal type RMS converter — 
the more common logarithmic computing type based instnimeats are 
inappropriate because their bandwidth is too low. 

The previously recommended high voltage probes are design^ to see 
a lMQ-10pF-22pF oscilloscope input. The RMS voltmeters have a 10 
meg Q, input. This difference necessitates an impedance matching net- 
work between the probe and the voltmeter. Details on this and other effi- 
ciency measurement issues appear in Appendix A, "Achieving 
Meaningful Efficiency Measurements." 



Layout 

The physical layout of the lamp, its leads, tte display housing, and other 
high voltage components, is an integral part of the circuit. Poor layout can 
easily degrade efficiency by 25%, and higher layout induced losses have 
been observed. Producing an optimal layout requires attention to how 
losses occur. Figure 1 1-22 begins our study by examining potential para- 
sitic paths between the transformer's output and the lamp. Parasitic capac- 
itance to AC ground from any point between the transformer output and 
the lamp creates a path for undesired current flow. Similarly, stray cou- 
pUng from any point along the lamp's length to AC ground induces para- 
sitic current flow. All parasitic current flow is wasted, causing the circuit 
to produce more energy to maintain the desired current flow in Dl and 
D2. The high- voltage path from the transformer to the display housing 
should be as short as possible to minimize losses. A good rule of thumb is 



164 



JimWHKams 



ORCWTBY 



/I 



/ - HV / 
/ LEAD WIRE y 




OfSPUYHOUSIMGAIMMX) 
RFIECTTV^ FOIL ON LAMP 



OUTPUT ^ 
CAPACITOR 

TYPiCALLY ^ \ 
I 15pF-47pF \ 



I ^\ '^N 



TO FEEDBACK 
CIRCUITRY 



.1 OESlReO 

1 aow I 



02 



to assume 1 % efficiency loss per inch of high voltage lead. Any PC board 
ground or power planes should be relieved by at least 14" in the high volt- 
age area. This not only prevents losses, bit eliminates arcing paths. 

Parasitic losses associated with lamp placement within the display 
housing require attention. High voltage wire length within the housing 
must be minimized, particularly for displays using metal construction. 
Ensiure tii^ the high voltage is apptied to the shortest wire(s) in the dis- 
play. This may require disassembling the display to verify wire length 
and layout. Another loss source is the reflective foil commonly used 
around lamps to direct light into the actual LCD. Some foil materials 
absorb considerably more field energy than others, creating loss. Finally, 
displays supplied in metal enclosures tend to be lossy. The metal absorbs 
significant energy and an AC path to ground is unavoidable. Direct 
grounding of a metal enclosed display further increases losses. Some 
display manufacturers have addressed this issue by relieving the metal in 
the lamp area with other materials. 

The highest efficiency "in system" backlights have been produced by 
eyeful attention to these issues. In some cases the entire display enclo- 
sure was re-engineered for lowest losses. 

Layout OMitidi^ions for Two-Lamp Designs 

Systems using two lamps have some unique layout problems. Almost 
all two lamp displays are color units. The lower light transmission char- 
acteristics of color displays necessitate more light. Therefore, display 
mamifacturers use two tubes to produce more light. The wiring layout of 
these two tube color displays affects efficiency and illumination balance 
in the lamps. Figure 1 1-23 shows an "x-ray" view of a typical display. 
This symmetrical arrangement presents equal parasitic losses. If CI and 
C2 and the lamps are matched, the circuit's current ou^ut splits evenly 
and equal illumination occurs. 



Rgufe11--22. 

Loss paths due to 
stray capacitance 
in a practical LCD 
installation. 
Minimizing these 
paths is essential 
for good efficiency 



165 



Tripping the Light Fantastic 




Figure 11-23. 

Loss paths for a 
"best case" dual 
lamp di^lay. 
Symmetry pro- 
motes balanced 
illumination. 



Figure 11-24's display arrangement is less friendly. The asymmetrical 
wiring forces unequal losses, and the lamps receive imbalanced current. 
Even with identical lamps, illumination may not be bal^ced. This con- 
dition is correctable by skewing CTs and C2*s values. CI, because it 
drives greater parasitic capacitance, should be larger than C2. This tends 
to equalize the currents, prorm>ting equal lamp drive. It is important 
to realize that this compensation does nothing to recapture the lost en~ 
ergy — efficiency is still compromised. There is no substitute for mini- 
mizing loss paths. 

In general, imbalanced illumination causes fewer problems than 
might be supposed. The effect is very difficult for the eye to detect at 
high intensity levels. Unequal illumination is much more noticeable 
at lower levels. In the worst case, the dimmer lamp may only partially 
illuminate. This phenomenon is discussed in detail in the section 
"Thermometering." 



Feedback Loop Stability Issues 

The circuits shown to this point rely on closed loop feedback to maintain 
the operating point. All linear closed loop systems require some form of 
frequency compensation to achieve dynamic stability. Circuits operating 
with relatively low power lamps may be frequency compensated simply 
by overdamping the loop. Figtii:es 11-18 and U-20use this approach. 
The higher power operation associated with color displays requires more 
attention to loop response. The transformer produces much higher output 



166 



Jim Williams 



DISPLAY HOUSING 




C1>C2F0R 
MiSMATCHEO 
PSTRAY 



voltages, particularly at start-up. Poor loop damping can allow trans- 
former voltage ratings to be exceeded, causing arcing and failure. As 
such, higher power designs may require optimization of transient 
response characteristics. 

Figure 11-25 shows the significant contributors to loop transmission 
in these circuits. The resonant Royer converter delivers information at 



Figure 11-24. 
Symmetric tosses 
in a dual lamp 
display. Skewing C1 
and C2 values 
compensates 
imbalanced loss 
paths, but not 
wasted energy 



HIGH VOLTAGE 



X 



CCFL LAMP t 



BALLAST 
CAPACITOR 



RESONANT 
ROYER 
-50kHz 



1/2 WAVE 
»56kHz 



-+V 



LT1172 

-100kHz 



FEEDBACK TERMINAL 



COMPEWSATiON 
-J- CAPACITOR 




RG 

AVERAGING 
TIME 

CONSTANT 



INTENSITY 
PWM CONTROL, 
TYPICALLY 1 kHz 



Figure 11-25. 

Delay terms in the 
feedback path. The 
RC time constant 
dominates loop 
transm'^ion delay 
and must be com- 
pensated for stable 
operation. 



167 



Tripping the Light Fantastic 



about 50kH2 to the lamp. This information is smoothed by the RC aver- 
aging time constant and delivered to the LTl 172*s feedback terminal as 
DC. The LTl 172 controls the Royer converter at a lOOkHz rate, closing 
the control loop. The capacitor at the LTl 172 rolls off gain, nominally 
stabilizing the loop. This compensation capacitor must roll off the gain 
bandwidth at a low enough value to prevent the various loop delays from 
causing oscillation. 

Which of these delays is the most significant? From a stability view- 
point, the LTl 172's output repetition rate and the Royer's oscillation 
frequency are sampled data systems. Their information delivery rate is 
far above the RC averaging time constant's delay and is not significant. 
The RC time constant is the major contributor to loop delay. This time 
constant must be large enough to turn the half wave rectified waveform 
into DC. It also must be large enough to average any intensity control 
PWM signal to DC. Typically, these PWM intensity control signals come 
in at a IkHz rate. The RC*s resultant delay dominates loop transmission. 
It must be compensated by the capacitor at the LTl 1 72. A large enough 
value for this capacitor rolls off loop gain at low enough frequency to 
provide stability. The loop simply does not have enough gain to oscillate 
at a frequency commensurate with the RC delay. 

This form of compensation is simple and effective. It ensures stability 
over a wide range of operating conditions. It does, however, have poorly 
damped response at system turn-on. At turn-on, the RC lag delays feed- 
back, allowing output excursions well above the normal operating point. 
When the RC acquires the feedback value, the loop stabilizes properly. 
This tum-on overshoot is not a concern if it is well within transformer 
breakdown ratings. Color displays, running at higher power, usually re- 
quire targe initial voltages. If loop damping is poor, the overshoot may be 
dangerously high. Figure 1 1-26 shows such a loop responding to 
tum-on. In this case the RC values are lOkQ and 4.7^f, with a 2\i{ com- 
pensation capacitor. Tum-on overshoot exceeds 3500 volts for over 10 



FtgtiriB 11-26. 

Destructive high 
voltage overshoot 
and ring-off due to 
poor loop compen- 
sation. Transformer 
failure and field 
recall are nearly 
certain. Job loss 
may also occur 



A= 1000V/DIV 




mm^mmf 



168 



Jim Williams 




Figure 11-27. 

Poor loop com- 
pensation caused 
this transformer 
failure. Arc oc- 
curred in higli 
voltage secondary 
(lower right). 
Resultant shorted 



turns caused 
overheating. 



milliseconds! Ring-off takes over 100 milliseconds before settling oc- 
curs. Additionally^ an inadequate (too small) ballast capacitor and exces- 
sively lossy layout force a 2000 volt output once loop settling occurs. 
This photo was taken with a transformer rated well below this figure. The 
resultant arcing caused transformer destruction, resulting in field failures. 
A typical destroyed transformer appears in Figure 1 1-27. 

Figure 1 1-28 shows the same circuit, with the RC values reduced to 
10kf2 and l^f. The ballast capacitor and layout have also been opti- 
mized. Figure 1 1-28 shows peak voltage reduced to 2.2 kilovolts with 
duration down to about 2 milliseconds. Ring-off is also much quicker, 
with lower amplitude excursion. Increased ballast capacitor value and 
wiring layout optimization reduce running voltage to 1300 volts. Figure 
1 l-29*s results are even better. Changing the compensation capacitor to a 
3kii-2^f network introduces a leading response into the loop, allowing 
faster acquisition. Now, turn-on excursion is slightly lower, but greatly 
reduced in duration. The running voltage remains the same. 

The photos show that changes in compensation, ballast value, and 
layout result in dramatic reductions in overshoot amplitude and duration. 
Figure 1 1-26's performance almost guarantees field failures, while 
Figures 1 1-28 and 1 1-29 do not overstress the transformer. Even with 



1000V/DIV 




Figure 11-28. 

Reducing RC time 
constant improves 
transient response, 
although peaking, 
ring-off, and run 
voltage are still 
excessive. 



HORIZ^Sros/DlV 

AM6TA22 



Tripping the Light Fai 



Rguw 11-29. 

Additional optimiza- 
tion of RC time 
constant and com- 
pensation capacitor 
reduces turn-on 
transient, Run 
voltage is large, 
indicating possible 
lossy layout and 
display. 



A=10pOV/DIV 




H0RIZ«2nisrt)IV 

the improvements, more margin is possible if display losses can be con- 
trolled. Figures 1 1-26-1 1-29 were taken with an exceptionally lossy 
display. The metal enclosure was very close to the foil wrapped lamps, 
causing large losses with subsequent high turn-on and running voltages. 
If the display is selected for lower losses, performance can be greatly 
improved. 

Figure 1 1-30 shows a low loss display responding to turn-on with 
a 2|if compensation capacitor and lOkii-lfif RC values. Trace A 
is the transformer's output while Traces B and C are the LTl 172's 
Vcompensation and feedback pins, respectively. The output overshoots 
and rings badly, peaking to about 3000 volts. This activity is reflected by 
overshoots at the Vcompensation pin (the LTl 172's error amplifier out- 
put) and the feedback pin. In Figure 11-31, the RC is reduced to lOkil- 
.l|lf. This substantially reduces loop delay. Overshoot goes dovm to only 
800 volts — a reduction of almost a factor of four. Duration is also much 
shorter. The Vcompensation and feedback pins reflect this tighter con- 
trol. Damping is much better, with slight overshoot induced at tum-on. 
Further reduction of the RC to lOkQ-.OlM-f (Figure 1 1-32) results in 
even faster loop capture, but a new problem appears. In Trace A, lamp 
mm on is so fast that the overshoot does not register in the photo. The 



FfguTill^. 

Mfavefonnisfora 
lower loss layQut 
and display. High 
votlage overshoot 
(TraceA)feFe' 
fleeted at ebmpen- 
sation node (Trace 
B) and feedback 
pin (Trace C). 



A=:2000V/DIV 



B*Q.5WDIV 



C=1Y/DIV 




HORIZ = 10msmiV 



Jim Williams 



Aa2CX}0V/DIV 



B»(15V/DIV 

C:»1V/DIV 




HORG:«^IOmsA)IV 



Rgure 11-31. 

Reducing RC time 
constant produces 
quick, clean loop 
behavior, Low loss 
layout and display 
result in 650 VRMS 
running voltage. 



Vconipensation (Trace B) and feedback nodes (Trace C) reflect this with 
exceptionally fast response. Unfortunately, the RC*s light filtering causes 
ripple to appear when the feedback node settles. As such, Figure 1 1-3 Ts 
RC values are probably more realistic for this situation. 

The lesson from this exercise is clear. The higher voltages involved in 
color displays mandate attention to transformer outputs. Under running 
conditions, layout and display losses can cause higher loop compliance 
voltages, degrading efficiency and stressing the transformer. At turn-on, 
improper compensation causes huge overshoots, resulting in possible 
transformer destruction. Isn't a day of loop and layout optimization 
worth a field recall? 



Extending Illumination Range 

Lamps operating at relatively low currents may display the '"thermometer 
effect," that is, light intensity may be nonuniformly distributed along 
lamp length. Figure 1 1-33 shows that although lamp current density is 
uniform, the associated field is imbalanced. The field's low intensity, 
combined with its imbalance, means that there is not enough energy to 
maintain uniform phosphor glow beyond some point. Lamps displaying 
the thermometer effect emit most of their light near the positive electrode, 
with rapid emission fall-off as distance from the electrode increases. 



A-2000V/DIV 

B«0.5V/[)!y 
G»1V/0IV 




HORlZ«10mVDIV 



Figure 11-32. 

Very low RC value 
provides even 
faster response, but 
ripple at feedback 
pin (Trace C) is 
too high. Figure 
11-31 is the best 
compromise. 



171 



Iripping the Light Fantastic 



Figure 11-33. 

Field strength vs. 

distance for a 
growKl referred 
lamp. Field imbal- 
ance promotes 
uneven illumination 
at low drive levels. 




Figure 11-34. 

The"tow 
thermometer" 
configuration. 



primary derived 
feedback balances 
tamp drive, extend^ 
ing dimming range. 



Placing a conductor along the lamp's length largely alleviates **thennome- 
tering." The trade-off is decreased efficiency due to energy leakage (see 
Note 4 and associated text). It is worth noting that various lamp types have 
different degrees of susceptibility to the thermometer effect. 

Some displays require an extended illumination range. **Thermome- 
tering" usually limits the lowest practical illumination level. One 
acceptable way to minimize '*thermometering" is to eliminate the large 



Q3 
TP0610 




^ 4.99k- 



T 



C1 - W(MAMKP-20 
01 . 02 ^ ZBEX ZTX849 Ofi ROHM 2SC5001 
LI .COILTROMCSCTX150-4 

• « 1% FIL M RESISTOR 

• • > StLtCT FOfl INPUT COMMON MODE RANGE INCLUDtS V)n 

DQ Ncrr suasTmm CM^PNENTS 

COILTRONICS (305) 781-^900, SUMlOA (706) 956-0666 



VlN 




E1 




LT1172 




E2 




GNO 





i T T'" 



:2mf 



1M4148 



33* 



iMPUT 



172 



field imbalance. Figure 1 1-34's circuit does this. This circuit's most sig- 
nificant aspect is that the lamp is fully floating — ^there is no galvanic con- 
nection to ground as in the previous designs. This allov^s Tl to deliver 
symmetric, differential drive to the lamp. Such balanced drive eliminates 
field imbalance, reducing thermometering at low lamp currents. This ap- 
proach precludes any feedback connection to the now floating output. 
Maintaining closed loop control necessitates deriving a feedback signal 
from some other point. In theory, lamp current proportions to Tl's or LI 's 
drive level, and some form of sensing this can be used to provide feed- 
back. In practice, parasitics make a practical implementation difficult.^ 

Figure 1 1-34 derives the feedback signal by measuring Royer con- 
verter current and feeding this information back to the LTl 172. The 
Royer's drive requirement closely proportions to lamp current under all 
conditions. Al senses this current across the .312 shunt and biases Q3, 
closing a local feedback loop. Q3's drain voltage presents an amplified, 
single ended version of the shunt voltage to the feedback point, closing 
the main loop. The lamp current is not as tightly controlled as before, but 
.5% regulation over wide supply ranges is possible. The dimming in this 
circuit is controlled by a IkHz PWM signal. Note the heavy filtering 
(33kfll~2]Lif) outside the feedback loop. This allows a fast time constant, 
minimizing turn-on overshoot.^ 

In all other respects, operation is similar to the previous circuits. This 
circuit typically permits the lamp to operate over a 40: 1 intensity range 
without "thermometering." The normal feedback connection is usually 
limited to a 10: 1 range. 

The losses introduced by the current shunt and Al degrade overall 
efficiency by about 2%. As such, circuit efficiency is limited to about 
90%. Most of the loss can be recovered at moderate cost in complexity. 
Figure 1 1-35's modifications reduce shunt and Al losses. Al, a precision 
micropower type, cuts power drain and permits a smaller shunt value 
without performance degradation. Unfortunately, Al does not function 
wbsn its inputs reside at the V+ rail. Because the circuit's operation re- 
quires this, some accommodation must be made."^ 

At circuit start-up, Al's input is pulled to its supply pin potential (actu- 
ally, slightly above it). Under these conditions, Al's input stage is shut 
off. Normally, ATs output state would be indeterminate but, for the am- 
plifier specified, it will always be high. This turns off Q3, permitting the 
LTl 172 to drive the Royer stage. The Royer's operation causes Ql's col- 
laetor swing to exceed the supply rail. This turns on the 1N4148, the 
BAT-85 goes off, and Al 's supply pin rises above the supply rail. This 
''bootstrapping" action results in Al's inputs being biased within the am- 



5. See Appendix C, "A Lot of Cut-Off-Ears and No Van Goghs — Some Not-So-Great Ideas," for 
details. 

6. See section **Feedback Loop Stability Issues." 

7. In otiier words, we need a hack. 



Tripping the Light Fantastic 



27pF -r" 7 10 




CI • WIMA MKP-20 
Q1 , 02 - ZETEX ZTX849 OR ROHM 2SC5001 
Ll.CCMLTRONlCSC"D(150-4 
T1-SUMCAEPS-207 

• = 1% FILM RESISTOR 

80 NOT Stl^nmE COillPONBITS 

COIlJRONtCS (005) 781-8900, SUMIDA (708) 956-0666 



Figure 11-35. 

The "low 
thermometer" 
circuit using a 
mfcropower, preci- 
sion topside sens- 
ing amplifier. 
Supply bootstrap- 
ping eliminates 
input common 
mode requirement, 
permitting a 1.6% 
efffciency gain. 









El 


LT1172 




E2 












GND 




Vc 



I 

i T 



1H4146 



2nF 



T 



1mf 



T 



0.03 



plifier's common mode range, and normal circuit operation commences. 
The result of all this is a 1.6% efficiency gain, permitting an overall cir- 
cuit efficiency of just below 92% . 

Epilogue 

Our understanding with Apple Computer gave them six months sole use 
of everything I learned while working with them. After that, we were 
free to disclose the circuit and most attendant details to anyone else, 
which we did. It found immediate use in other computers and applica- 
tions, ranging from medical equipment to automobiles, gas pumps, retail 
terminals and anywhere else LCD displays are used. The development 
work consumed about 20 months, ending in August, 1993, Upon its 
completion I inmiediately fell into a rut, certain I would never do any- 
thing worthwhile again. 



174 



JimWiftiams 



{Terences 

1 . Blake, James W. The Sidewalks of New York. (1 894). 

2. Bright, Httman, and Royer, "Transistors As On-Off Switches in Saturable Core 
Ckmiisr Electrical Manufacturing (December 1954): Available from Technomic 
Biblishing, Lancaster, PA. 

3. Sharp CoTpOTBtion. Flat Panel Dispiays. (1991). 

4. Kitchen, C. , and L. Counts. RMS-to-DC Conversion Guide, Analog Etevices, Inc. 

(1986). 

5. Williams, Jim. "A Monolithic IC for lOOMHz RMS-DC Conversion." Linear 
Technology Corporation, Application Note 22 (September 1 987). 

6. Hewlett-Packard. "1968 Imtruftiemation. K 
mt&ge Measurement (1 968): 197-198. 

7. Hewlett-Packard. Model 3400RMS Voltmeter Operating and Service Manual. 

(1965). 

8 . Hewlett-Packard. Model 3403C True RMS Voltmeter Operating and Service 
Mmual. (1973). 

9. Ott, W E. "A New Technique of Thermal RMS Measurement.'' IEEE Journal of 
Solid State Circuits (December 1974). 

10. Williams, J.M.» and T.L. Longman. "A 25MHz Thermally Based RMS-DC 
Converter." IEEE ISSCC Digest of Technical Papers (1986). 

1 1 . O'Neill, PM. "A Monolithic Thermal Converter." H.R Journal (May 1980). 

12. Williams, L "Thermal Technique in Measurement and Control Circuitry," "50MH2 
Thermal RMS-DC Converter." Linear Technology Corporation, Application Note 5 

(December 1984). 

13. Williams, J., and B. Huffman. "Some Thoughts on DC- DC Converters": Appendix 
A, "The +5 to 10 ±15V Converter— A Special Case." Linear Technology 
Corporation, Application Note 29 (October 1 988). 

1 4. Baxendall, PJ. 'Transistor Sine- Wave LC Oscillators." British Journal of IEEE 
(February 1960): Paper No. 2978E. 

15. Williams, J. 'Temperature Controlling to Microdegrees." Massachusetts Institute of 
Technology, Education Research Center (1971): out of print. 

16. Fulton, S.P. 'The Themaal Enzyme Probe." Thesis, Massachusetts Institute of 

Technology (1975). 

1 7. Williams, J. "Designer's Guide to Temperature Measurement." EDN part II (May 
20,1977), 

18. Williams. J. "Illumination Circuitry for Liquid Crystal Displays." Linear 
Technology Corporation, Application Note 49 (August 1 992). 

19. Olsen, J.V. "A High Stability Temperature Controlled Oven." Thesis, Massachusetts 

institute of Technology ( 1974). 

20. MIT Reports on Research. The Ultimate Oven. (March 1972). 

2 1 . McDermoit, James. *Test System at MIT Controls Temperature of Microdegrees." 
Electronic Design {Jmmr^ 6 

22. Wilhams, Jim. "Techniques for 92% Efficient LCD Illumination." Linear 
Technology Corporation, Application Note 55 (August 1993). 



175 



Tripping the Light Fantastic 



Appendix A 

Achieving Meaningful Efficiency 

Obtaining reliable efficiency data for the CCFL circuits presents a high 
order difficulty measurement problem. Establishijag and nmiiitainiag 
accurate AC measurements is a textbook example of attention to mea- 
surement technique. The combination of high frequency, harmonic laden 
waveforms and high voltage makes meaningful results difficult to obtain. 
The choice, understanding, and use of test instruni^ation is crucial. 
Clear thinking is needed to avoid unpleasant surprises!^ 

Probes 

The prolDes employed must faithfully respond over a variety of conditions. 
Measuring across the resistor in series with the CCFL is the most favor- 
able circumstance. This low voltage, low impedance measurement allows 
use of a standard IX probe. The probe's relatively high input capacitance 
does not introduce significant erron A lOX iH"obe may also be but 
frequency compensation issues (discussion to follow) must be attended to. 

The high voltage measurement across the lamp is considerably more 
demanding on the probe. The waveform fundamental is at 2{BcHz to 
lOOkHz, with harmonics into the MHz region. This activity occurs at 
peak voltages in the kilovolt range. The probe must have a high fidelity 
response under these conditions. Additionally, the probe should have low 
input capacitance to avoid loading effects which would cornq>t the mea- 
surement. The design and construction of such a probe requires signifi- 
cant attention. Figure 1 1-Al lists some recommended probes along with 
their characteristics. As stated in the text, almost all standard oscilloscope 
probes will fail^ if used for this measurement. Attemptii^ to citcomvesnt 
the probe requirement by resistively dividing the lamp voltage also cre- 
ates problems. Large value resistors often have significant voltage coeffi- 
cients and their shunt capacitance is high and uncertain. As such, simple 
voltage dividing is not recommended. Similarly, common high voltage 
probes intended for DC measurement will have large errors because of 
AC effects. The P6013A and P60I5 are the favored probes; their lOOMa 
input and small capacitance introduces low loading error* The penalty for 
their lOOOX attenuation is reduced output, but the recommended volt- 
meters (discussion to follow) can accommodate this. 

All of the recommended probes are designed to work iiHo an iSacillo- 
scope input. Such inputs are almost always IMQ paralleled by (typically) 



1 . It is worth considering that various constructors of Figure 1 1-18 have reported efl^laieici 
ranging from 8% to 115%. 

2. That*s twice Tve warned you nicely. 



176 



10pF-22pF. The recommended voltmeters, which will be discussed, have 
significantly different input characteristics. Figure 1 1-A2's table shows 
higher input resiiilaflces and a range of capacitances. Because of this the 
probe must be compensated fox the voltmeter's input characteristics. 
Normally, the oplinium compensation point is easily determined and 
adjusted by observing probe output on an oscilloscope, A known- 
amplitude square wave is fed in (usually from the oscilloscope calibrator) 
and the probe adjusted for correct response. Using the probe with the 
voltmeter presents an unknown impedance mismatch and raises the prob- 
lem of detenmning when compensation is correct. 

The impedance mismatch occurs at low and high fFequency. The low 
frequency termis corrected by placing an appropriate value resistor in 
shunt with the probe's output. For a lOMQ voltmeter input, a 1 . IMQ 
resistor is suitable. This resistor should be built into the smallest possible 
BNC equipped enclosure to maintain a coaxial environment. No cable 
connections should be employed; the enclosure should be placed directly 
between the probe output and the voltmeter input to minimize stray ca- 
pacitance. This arrangement compensates the low frequency impedance 
mismatch. Figure 1 1-A4 shows the impedance-matching box attached to 
the high voltage probe. 

Correcting the high frequency mismatch term is more involved. The 
wide range of voltmeter input capacitances combined with the added 
shunt resistor's effects presents problems. How is the experimenter to 
know where to set ttie high frequency probe compensation adjustment? 
One solution is to feed a known value RMS signal to the probe- voltmeter 
combination and adjust compensation for a proper reading. Figure 1 1-A3 
shows a way to generate a known RMS voltage. This scheme is simply a 
standard backlight circuit reconfigured for a constant voltage output. The 
op amp permits low RC loading of the 5 .6K feedback termination without 
introducing bias current error. The 5.6kQ value may be series or parallel 
trimmed for a 300V output. Stray parasitic capacitance in the feedback 
network affects output voltage. Because of this, all feedback associated 
nodes and components should be rigidly fixed and the entire circuit built 
into a small metal box. This prevents any significant change in the para- 
sitic temas. The result is a known SOOVr^s output. 

Now, the probe's compensation is adjusted for a 300V voltmeter indi- 
cation, using the shortest possible connection (e.g., BNC-to-probe 
adapter) to the calibrator box. This procedure, combined with the added 
lesistor, completes the probe-to- voltmeter impedance match. If the probe 
compensation is altered (e.g., for proper response on an oscilloscope) the 
voltmeter's reading will be erroneous.'^ It is good practice to verify the 



3. The translation of this statement is to hide the probe when you are not using it. If anyone wants 
to borrow it, look straight at them, shrug your shoulders, and say you don't know where it is. 
This is decidedly dishonest, but eminently practical. Those finding this morally questionable may 
wish to reexamine their attitude after producing a day's worth of worthless data with a probe that 
was unknowingly readjusted. 



Figure 11-^A1. 

Characteristics of 
some wideband 
high voltage 
probes. Ou^ut 
impedances are 
designed for oscil- 
loscope inputs. 



TEKTRONIX 


















DERATED TO 




ASSUMED 


PROBE 


AHENUATION 




INPUT 


INPUT 


RISE 


BAND- 


MAXIMUM 


DERATED 


AT 


COMPENSATION 


TERMINATION 


TYPE 


FACTOR 


ACCURACY 


RESISTANCE 


CAPACITANCE 


TIME 


WIDTH 


VOLTAGE 


ABOVE 


FREQUENCY 


RANGE 


RESISTANCE 


P6007 


100X 


3% 


10Mn 


2.2pF 


14ns 


25MHz 


1.5kV 


200kHz 


700VRMS 
at 10 MHz 


15-55pF 


1M 


P6009 


100X 


3% 


10MQ 


2,5pF 


2.9ns 


120MHz 


1.5kV 


200kHz 


45QVRMS 
at 40MHz 


15-47pF 


1M 


P6013A 


1000X 


Adjustable 


100MQ 


3pF 


7ns 


50MHz 


12kV 


100kHz 


SOOVrms 
at 20MHz 


12-60pF 


1M 


P6015 


1000X 


Adjustable 


lOOMQ 


3pF 


1.4ns 


250MHz 


20kV 


100kHz 


2000VRMS 
at 20MHz 


12-47pF 


1M 



Figure 11-A2. 

Pertinent character- 
istics of some 
thermally based 
RMS voltmeters. 
Input impedances 



ing network and 
compensation for 
high voltage 



MANUMCTURER 
AND MODEL 


FULL SCALE 
RANGES 


ACCURACY 
AT 1MHz 


ACCURACY 
AT 100kHz 


INPUT RESISTAHCE 
AND CAPACITANCE 


BAN0IDTH 


CREST 
FACTOR 


Hewlett-Packard 3400 
Meter Display 


1mVto300V, 
12 Ranges 


1% 


t% 


0.001V to 0.3V Range == 1 0M and < 50pF, 
t V to 300V Range - 10M and < 20pF 


10MHz 


10:1 At Full Scale, 
100:1 At 0.1 Scale 


Hewlett-Packard 3403C 
DtQHaf Display 


10mV to 1000V, 
6 Ranges 


0.5% 


0.2% 


1 0mV and 1 0OmV Range = 20M and ±10%, 
IV to 1000V Range - 10M and 24pF i10% 


100MHz 


10:1 At Full Scale. 
100-1At0.1Scai» 


Fluke 8920A 
Oiffiai Display 


2mVlo70QV, 
7Ranges 


07% 


0.5% 




20MHz 


7.1 At Full Scale 
/0.rAl0.1Sc9ie 



JrmWitliams 



75k to 3W 
CARBON COMP 



SHORT WIRE DIRECTLY 
TfiTHISBNC OUTPUT 

^ OUTPUT -60kHz 




Figure 11-A3. 

High voltage RMS 
calibrator is voltage 
output vejwi of 
CCFL circuit. 



CI = MUST BE A LOW LOSS CAPACITOR. 
METALIZEO POIYCARB 

WIMA FKP2 OR MKP-20 (GERMAN) RECOWMFNDED 
L1 =SUMIDA 6345-020 OR C0ILTR0NICSCTX11 0092-1 

PIN NUMBERS SHOWN FOR COiLTRONIGS UNIT 
L2 = C01LTRONICSCTX300-4 
Q1 , 02 - AS SHOWN OR BCP 56 (PHILLIPS SO PACKAGE) 

* = 'i% FILM RESISTOR (lOkaTO 75kt2 RESISTORS IN SERIES) 
DO NOT SUBSTITUTE COMPONENTS 

COILTRONICS (305) 781 -8900, SUMIDA (708) 956-0666 

calibrator box output before and after every set of efficiency measure- 
nients. This is done by directly connecting, via BNC adapters, the calibra- 
tor box to the RMS voltmeter on the lOOOV range. 

RMS Voltmeters 



The efficiency measurements require an RMS responding voltmeter. This 
instrument must respond accurately at high frequency to irregular and 
harmonically loaded waveforms. These considerations eliminate almost 
all AC voltmeters, including DVMs with AC ranges. 



179 



Tripping the Light Fantastic 



Figure 11-A4. 

The impedance 
matching box 
(extreme left) 
mated to the high 
voKage probe. Note 
direct connection. 
No cable is used. 




There are a number of ways to measure RMS AC voltage. Three of the 
most common include average, logarithmic, and thermally responding. 
Averaging instruments are calibrated to respond to the average value of 
the input waveform, which is ahnost always assumed to be a sine wave. 
Deviation from an ideal sine wave input produces errors* Logarithmically 
based voltmeters attempt to overcome this limitation by continuously 
computing the input's true RMS value. Although these instruments are 
"real time" analog computers, their 1 % error bandwidth is well below 
300kHz and crest factor capability is limited. Almost all general purpose 
DVMs use such a logarithmically based approach and, as such, are not 
suitable for CCFL efficiency nneasurements. Thermally based RMS volt- 
meters are direct acting thermo-eiectronic analog computers. They 
respond to the input*s RMS heating value. This technique is explicit, 
relying on the very definition of RMS (e.g., the heating power of the 
waveform). By turning the input into heat, thermally based instruments 
achieve vastly higher bandwidth than other techniques,"* Additionally, 
they are insensitive to waveform shape and easily accommodate large 
crest factors. These characteristics are necessary for the CCFL efficiency 
measurements. 

Figure 1 1-A5 shows a conceptual thermal RMS-DC converter. The 
input waveform warms a heater, resulting in increased output fix)m its 
associated temperature sensor. A DC amplifier forces a second, identical, 
heater-sensor pair to the same thermal conditions as the input driven pair. 
This differentially sensed, feedback enforced loop makes ambient tem- 
perature shifts a common mode term^ eliminating their effect. Also, al- 
though the voltage and thermal interaction is non-linear, the input-output 
RMS voltage relationship is linear with unity gain. 

The ability of this arrangement to reject ambient temperature shifts 
depends on the heater-sensor pairs being isothermal. This is achievable by 
thermally insulating them with a time constant well below that of ambient 
shifts. If the time constants to the heater-sensor pairs are matched, ambi- 
ent temperature terms will affect the pairs equally in phase and amplitude. 



4. Those finding these descriptions intolerably brief are commended to references 4, 5. and 6 



JtmWHIiams 



DC AMPLIFIER 




Figure t1-A5. 
Conceptual thermal 
RMS-DC converter. 



The DC amplifier rejects this common mode term. Note that, although the 
pairs are isothermal, they are insulated from each other. Any thermal in- 
teraction between the pairs reduces the system's thermally based gain 
terms. This would cause unfavor^le signal-to-noise performance, limit- 
ing dynamic operating range. 

Figure ll-A5's output is linear because the matched thermal pair's 
nonlinear voltage-temperature relationships cancel each other. 

The advantages of this approach have made its use popular in ther- 
mally based RMS-DC measurements. 

The instruments listed in Figure 11-A2, while considerably more ex- 
pensive than other options, are typical of what is required for meaningful 
resiilts. The HP3400A and the Fluke 8920A are currently available from 
their manufacturers. The HP3403C, an exotic and highly desirable instru- 
ment, is no longer produced but readily available on the secondary market. 

Figure 1 1-A6 shows equipment in a typical efficiency test setup. The 
RMS voltmeters (photo center and left) read output voltage and current 
via high voltage (left) and standard IX probes (lower left). Input voltage 
is read on a DVM (upper right). A low loss clip-on ammeter (lower right) 
determines input current. The CCFL circuit and LCD display are in the 
foreground. Efficiency, the ratio of input to output power, is computed 
with a hand held calculator (lower right) . 

Catorimetric Correlation of Electrical Efficiency 
MMiiir^nts 

Careful measurement technique permits a high degree of confidence in the 
accuracy of the efficiency measurements. It is, however, a good idea to 
check the method's integrity by measuring in a completely different do- 
main. Figure 11-A7 does this by calorimetric techniques. This arrange- 
ment, identical to the thermal RMS voltmeter's operation (Figure 1 1-A5), 



181 



Tripping the Light Fantastic 



Figure 11-A6. 

Typical efficiency 
measurement 
instrumentation, 
RMS voltmeters 
(center left) mea- 
sure output voltage 
and current via 
appropriate probes. 
Clip-on ammeter 
(right) gives low 
loss input current 
readings. DVM 
(upper right) mea- 
sures input voltage. 
Hand calculator 
(lower right) is 
used to compute 
efficiency 




Rgur«11-A7. 

Efficiency 
determination via 
caforimetric mea- 
surement. Ratio 
of power supply 
to output energy 
gives efficiency 
information. 



determines power delivered by the CCFL circuit by measuring its load 
temperature rise. As in the thermal RMS voltmeter, a differential approach 
eliminates ambient temperature as an error term. The differential ampli- 
fier's output, assuntiing a high degree of matching in the two thermal en- 
closures, proportions to load power. The ratio of the two cells' E x I 
products yields efficiency information. In a 100% efficient system, the 
amplifier's output energy would equal the power supplies' output. 
Practically it is always less, as the CCFL circuit has losses. This term 
represents the desired efficiency information. 

Figure 1 1-A8 is similar except that the CCFL circuit board is placed 
within the calorimeter. This arrangement nominally yields the same in- 
formation, but is a much more demanding measurement because far less 
heat is generated. The signal-to-noise (heat rise above ambient) ratio is 
unfavorable, requiring almost fanatical attention to thermal and instm- 



m 




THERMALLY INSULATED EMCLOSUBE 



HIGH 
I --THERMAL - 

f 

I. 



mm -L 



TEMPERATURE 
SENSOR 




OUTPUT I 



•otrrpury 



JlmWIIfiams 



. THERMAllv rtJSULATED ENCLOSURE 



I3SBB!BIE5H ! 



ICCaCfBGUITj 



TEMPERATURE 
SENSOR 



HIGH 
-^THERMAL 
RESISTANCE 



HEATER 



1. 



TEMPERATURE 

SENSOR 



mentation considerations,^ It is significant that the total uncertainty be- 
tween electrical and both calorimetric efficiency determinations was 
3.3%. The two thermal approaches differed by about 2%. Figure 1 1-A9 
shows the calorimeter and its electronic instrumentation. Descriptions of 
this instrumentation and thermal measurements can be found in the 
References section following the main text. 




OUTPUT I 

*(aiTwnv 



FiguiBlVAS. 

The calorimeter 
measures effi- 
ciency by \ 
ing circuit heating 
losses 



5. Calorimetric ineasurements aie not recommended for readers who are short on time or sanity. 




Figure 11-A9. 

The catorimeter 
(center) and Its 
instrumentation 
(top). Calorimeter's 
high degree of 
themial symmetry 
combined with 
sensitive servo 
instrumentation 
produces accurate 
efficiency measure- 
ments. Lower 
portion of photo is 
calorimeter's top 
cover 



Tripping the Light Fantastic 

Appendix B 

Photometric Measurements 

In the final analysis the ultimate concern centers around the efficient 
conversion of power supply energy to light. Emitted light varies monoto- 
nically with power supply energy/ but certainly not linearly. In particu- 
lar, bulb luminosity may be highly nonlinear, particularly at high power, 
vs, drive power There are complex trade-offs involving the amount of 
emitted light vs. power consumption and battery life. Evaluating these 
trade-offs requires some form of photometer. The relative luminosity of 
lamps may be evaluated by placing the lamp in a light tight tube and 
sampling its output with photodiodes. The photodiodes are placed along 
the lamp's length and their outputs electrically sunmied. This sampling 
technique is an uncalibrated measurement, providing relative data only. It 
is, however, quite useful in determining relative bulb emittance under 
various drive conditions. Figure 1 1-Bl shows this *'glometer,** with its 
uncalibrated output appropriately scaled in "brights," The switches allow 
various sampling diodes along the lamp's length to be disabled. The pho- 
todiode signal conditioning electronics are mounted behind the switch 
panel. 

Calibrated light measurements call for a tme photometer. The 
Tektronix J-17/J1803 photometer is such an instrument. It has been found 




Figure 11-Bt 

The "glometer" measures relative lamp emissivity. CCFL circuit mounts to the right. Lamp is insitte cylindrical 
housing. Photodiodes (center) convert light to electrica! output (lower left) via amplifiers (not visible in photo). 



1 . But not always! It is jjossibie to build highly electrically efficient ciicuits that emit less light than 
"less efficient" designs. See Appendix C. ' A Lot of Cut-OfFEars and No Van Goghs— Some 
Not-So-Great Ideas " 



Jim Wifliams 



particularly useful in evaluating display (as opposed to simply the lamp) 
luminosity under various drive conditions. The calibrated output permits 
reliable correlation with customer results.^ The light tight measuring head 
allows evaluation of emittance evenness at various display locations. This 
capability is invaluable when optimizing lamp location and/or ballast 
capacitor values in dual lamp displays. 

Figure 1 1-B2 shows the photometer m use evaluating a display. 



2. It is unlikely that custoiners would be enthusiastic about correlating the "brights'* units produced 
by the aforementioned glometer 




Figure 11-B2. 

Apparatus for calibrated photomfitric display evaluation. Photometer (upper right) indi- 
cates display luminosity via sensing head (center). CCFL cifcurt (left) intensity is con- 
trolled by a calibrated pulse width generator (upper left). 



Trtppktg the Light Fantastic 



Appendix C 

A Lot of Cut-Off Ears and No Van Goghs— Some 
Not-So-Great ideas 

The hunt for a practical CCFL power supply covered (and is still cover- 
ing) a lot of territory. The wide range of conflicting requirements com- 
bined with ill-defined lamp characteristics produces plenty of unpleasant 
surprises. This section presents a selection of ideas that turned into disap- 
pointing breadboards. Backlight circuits are one of die deadliest places 
for theoretically interesting circuits the author has ever encountered. 

Not-So-Great Backlipt Circuits 

Figure 11-Cl seeks to boost efficiency by eliminating the LT1172's satu- 
ration loss. Comparator CI controls a free running loop around tlie Rayer 
by on-off modulation of the transistor base drive. The circuit delivers 
bursts of high voltage sine drive to the lamp to maintain the feedback 



Figure 11-C1. 

A first attempt at 
improving the basic 
circuit. Irregular 
Royer drive pro- 
motes losses and 
poor regulation. 




186 



Jim Williams 



node. The scheme worked, but had poor line rejection, due to the varying 
waveform vs. supply seen by the RC averaging pair. Also, the "burst" 
modulation forces the loop to constantly re-start the bulb at the burst rate, 
wasting energy. Finally, bulb power is delivered by a high crest factor 
waveform, causing inefficient current-to-light conversion in the bulb. 

Figure 1 1-C2 attempts to deal with some of these issues. It converts 
the previous circuit to an amplifier-controlled current mode regulator. 
Also, the Royer base drive is controlled by a clocked, high frequency 
pulse width modulator. This arrangement provides a more regular wave- 
form to the averaging RC, improving line rejection. Unfortunately the 
improvement was not adequate. 1 % line rejection is required to avoid 
annoying flicker when the line moves abruptly, such as when a charger is 
activated. Another difficulty is that, although reduced by the higher fre- 
quency PWM, crest factor is still non-optimal. Finally, the lamp is still 
forced to restart at each PWM cycle, wasting power. 

Figure 1 1-C3 adds a "keep alive" function to prevent the Royer from 
turning off. This aspect worked well. When the PWM goes low, the 
Royer is kept running, maintaining low level lamp conduction. This eUm- 
inates the continuous lamp restarting, saving power. The "supply correc- 



REUTIVELY HIGH j*" 



FREQUENCY^ 



L_J ~1_ 




Figure 11-C2. 

A more sophisti- 
cated failure still 
has losses and 
poor line regujj^on. 



187 



Tripping the Light Fantastic 



RELATI\a.Y HIGH J" 



FREQUENCY , 



L_J l_J 1- 



J— HI 

WIDTH KEEP ALIVE 



Figure 11-C3. 

"Keep alive" circuit 
eliminates turn-on 
losses and has 
94% efficiency. 
Light emission is 
lower than "less 
efficienf circuits. 




SllPPiY 
COBREGTION 



-+V 



tion" block feeds a portion of the supply into the RC averager^ improving 
line rejection to acceptable levels. 

This cireuit, after considerable fiddling, achieved almost 94% effi- 
ciency but produced less output light than a '*less efficient" version of 
Figure 1 1-18! The villain is lamp waveform crest factor. The keep alive 
circuit helps, but the lamp still cannot handle even moderate crest factors. 

Figure 1 1-C4 is a very different approach. This circuit is a driven 
square wave converter. The resonating capacitor is eliminated. The base 
drive generator shapes the edges, minimizing harmonics for low noise 
operation. This circuit works well, but relatively low operating frequen- 
cies are required to get good efficiency. This is so because the sloped 
drive must be a small percentage of the fundamental to maintain low 
losses. This mandates relatively large magnetics — a crucial disadvantage. 
Also, square waves have a different crest factor and rise time than sines, 
forcing inefficient lamp transduction. 



188 



JlmWitliaiDS 



CONTROLLED 
AV/AT EDGES 



7a LAMP AND 
FKDBACK PATH 



CONTROLLED 
AV/AT EDGES 



SHAPEDDRIVE 
GENERATOR 



CLOCK FROM 
LTH72 



TO 
LT1172 

-FROM 
LT1172 



Figure 11 -C4, 
A non-resonant 
approach. Stew 
retarded edges 
minimize harmon- 
ics, buttiBn^rrner 
size goes up. 
Output waveform 
is also non-optimal, 
causing lamp 
losses. 



1^ Primary Side Sensing Ideas 



Figures 1 1-34 and 1 1-35 use primary side current sensing to control 
bulb intensity. This permits the bulb to fully float, extending its dynamic 
operating range. A number of primary side sensing approaches were tried 
before the "topside sense" won the contest. 

Figure 1 1-C5's ground referred current sensing is the most obvious 
way to detect Royer current. It offers the advantage of simple signal con- 
ditioning — ^there is no common mode voltage. The assumption that es- 
sentirily all Royer current derives from the LTl 172 emitter pin path is 
true. Also true, however, is that the waveshape of this path's current 



CURRENT 
FROM ROYER 




LOW 

RESISTANCE 
SHUNT 



Figure 11 -C5. 

''Bottom side" 
current sensing has 
poor line regulation 
due to WD averag- 
ing characteristics. 



189 



Tripping the Light Fantastic 



Figure 11-C6. 

Flux sensing has 
irregular outputs, 
particularly at 
low currents. 



varies widely with input voltage and lamp operating current. The RMS 
voltage across the shunt (e.g., the Royer current) is unaffected by this, 
but the simple RG averager produces different outputs for the various 
waveforms. This causes this approach to have very poor line rejection, 
rendering it impractical. Figure 1 1-C6 senses inductor iux, which 
should correlate with Royer current. This approach promises attractive 
simplicity. It gives better line regulation but still has some trouble giving 
reliable feedback as waveshape changes. It also, in keeping with most 
flux sampling schemes, regulates poorly under low current conditions. 

Figure 11-C7 senses flux in the transformer. This takes advantage of 
the transformer's more regular waveform. Line regulation is reasonably 
good because of this, but low current regulation is still poor. Figure 11~G8 
samples Royer collector voltage capacitively, but the feedback signal does 
not accurately represent start-up, transient, and low current conditions. 

Figure 1 1-C9 uses optical feedback to eliminate all feedback integrity 
problems. The photodiode-amplifier combination provides a IXI feed- 
back signal which is a function of actual lamp emission. It forces the 
lamp to constant emissivity, regardless of environmental or aging factors. 

This approach works quite nicely, but introduces some evil problems. 
The lamp comes up to constant emission immediately at tum-on. There is 
no warm-up time required because the loop forces emission, instead of 
current. Unfortunately, it does this by driving huge overcurrents through 
the lamp, stressing it and shortening life. Typically, 2 to 5 times rated 
current flows for many seconds before lamp temperature rises, allowing 
the loop to back down drive. A subtle result of this effect occurs with 
lamp aging. When lamp emissivity begins to fall off, the loop increases 
current to correct the condition. This increase in current accelerates lamp 
aging, causing further emissivity degradation. The resultant downward 
spiral continues, resulting in dramatically shortened lamp life. 



CURRENT 
FROM ROYER 




LT1172 



FB 



AAA 1^ 



INTENSITY 
CONTROL 



GND 



E1 



E2 



X 




190 



JimWtHidfns 



Other problems involve increased component count, photodiode 
mounting, and the requirement for photodiodes with predictable response 
or some form of trim. 

TO LAMP 
AND FEEDBACK 



+v 



r'''^'^"'^^""^ FLUX SENSE 
-J- WINDING 



X 



I \AfL \^ INTENSITY 
^^"''VVV-t^^ CONTROL 



+V 



TO 
LT1172 



TO 
LT1172 
FB PIN 



Figure 11-C7. 
Transformer flux 
sensing gives more 
regular feedback, 
but not at low 
currents. 




j^^^y^^ INTENSITY 



CONTROL 



Figure 11-C8. 

AC couples drive 
waveform feedback 
is not reliable at low 
currents. 



HIGH VOLTAGE 
DRIVE 



T0LT1172 
FEEDBACK PIN 




BALLAST 
CAPACITOR 



LAMP 



Ftgum 11-C9. 

Optically sensed 
feedback elimi- 
nates feedback 
irregularities, but 
introduces other 
problems. 



191 



Tripping the Light Fantastic 



Appendix D 

Perspectives on Efficiency 

The LCD displays currently available require two power sources, a back- 
light supply and a contrast supply. The display backlight is the single 
largest power consumer in a typical portable apparatus, accounting for 
almost 50% of the battery drain when the display intensity con&t)l is at 
maximum. Therefore, every effort must be expended to maximize back- 
light efficiency. 

The backlight presents a cascaded energy attenuator to the battery 
(Figure 1 1-Dl). Battery energy is lost in the electrical-to-electricai con- 
version to high voltage AC to drive the cold cathode fluorescent lamp 
(CCFL). This section of the energy attenuator is the most efficient; con- 
version efficiencies exceeding 90% are possible. The CCRL, although 
the most efficient electrical-to-light converter available today, has losses 
exceeding 80%. Additionally, the light transmission efficiency of present 
displays is about 10% for monochrome, with color types even lower. 
Clearly, overall backlight efficiency improvements must come from bulb 
and display improvements. 

Higher CCFL circuit efficiency does, however, directly translate into 
increased operating time. For comparison purposes Figure 1 1-20's circuit 
was installed in a computer running 5mA lamp current. The result was a 
19 minute increase in operating time. 

Relatively small reductions in backlight intensity can greatly extend 
battery life. A 20% reduction in screen intensity results in nearly 30 min- 
utes of additional running time. This assumes that efficiency remains 
reasonably flat as power is reduced. Figure 1 1-D2 shows that the cir- 
cuits presented do reasonably well in this regard, as opposed to other 
approaches. 

The contrast supply, operating at greatly reduced power, is not a major 
source of loss. 



Figure 11-D1. 

The backlit LCD 
display presents a 
cascaded energy 
attenuator to the 
battery. DC to AC 
conversion Is signif- 
icantly more effi- 
cient than energy 
conversions in 
lamp and display. 



ELECTRICAL TO 
ELECTRICAL 
CONVERSfON 



BATTERY 



DC TO AC 
HIGH VOLTAGE 
CONVERTER 



ELECTRICAL TO 




LIGHT TO 


LIGHT 




LIGHT 


CONVERSION 




CONVERSION 


COLD CATHODE 






FLUORESCENT 




LCD 


LAMP 




DISPLAY 


(CGFL) 







> 90% EFFICIENT 



< 20% EFFICIENT 

OUTPUT TYPICALLY 
1500VAC TO START, 
350VacTO RUN AT 
5mA-10mA OUTPUT 



: 10% EFFICIENT 



192 



JimWttiams 











FEXT FIGURE 21 


















1 — 1 
















_ _ ^ 




























TYPICAL 
















MODULE 


-M 
OF 


1 


1 

30ES N( 
IW 7HIS 


3T 
















\TE 


■A 
















-i 










- 


































tI 


i 






! 


.J 





0.5 



1 1.5 2M 
POWER OUT (W) 



2^ 3,0 



Figure 11 -D2. 

Efficiency compari- 
son between Figure 
11-21 and a typical 
modular converter. 



193 



This page intentionally left blank 



Part Three 

Selling It 



One of the ch^cteristics of a good design is that somebody wants to use 
it. In today's world this means it must be saleable. Doug Grant's "Analog 
Circuit Design for Fun and Profit" addresses a circuit specification often 
ignored or poorly handled by designers — is the circuit saleable? Does 
anyone want it; and will they select it over other alternatives? This chap- 
ter should be required reading for anyone hired into a design position. 

Bob Reay describes selling another "design," namely yourself. His 
chapter, "A New Graduate's Guide to the Analog Interview," should be 
required reading for anyone trying to get hired into a design position. 

The section ends with the story of the most famous timekeeper in his- 
tory, John Harrison's marine chronometer. It may also be the biggest mar- 
keting nightmare in history. This is a lesson in the tenacity required for 
technical and economic success in the face of an almost intractable tech- 
nical problem and human foibles, Harrison's stunning accomplishment 
combined craft, geirius, and singular, uninterrupted dedication to produce 
a solution the world very badly wanted. His task was not, however, insu- 
lated from human failings. Imagine spending a lifetime to give the world 
exactly what it asked for and still needing the king of England's help to 
get paid ! 



195 



This page intentionally left blank 



Doug Grant 



12. Analog Circuit Design for 

Fun and Profit 



The first volume of this series of books deah mainly with how to design 
analog circuits. It was an interesting collection of ideas, anecdotes, and 
actual descriptions of the processes used by various well-known ana- 
log circuit designers to accomplish their goals. You won't find much of 
that sort of thing in this chapter (although I hope it will be interesting 
nonetheless). 

The inspiration for this chapter arose in part from a comment in the 
chapter of the first book submitted by Derek Bowers of Analog Devices. 
He admitted that some of his most elegant circuits turned out to be poor 
sellers, while other circuits (of which he was not particularly proud) be- 
came multi-million-dollar successes. In this chapter, I will offer a few 
words of advice to fledgling analog design engineers in an effort to help 
them distinguish between good circuits and good products. In addition, 
I'll alert fledgling circuit designers to a new person they will eventually 
encounter in their careers — the Marketeer. 

Why I Wanted to Be an Engineer 

As an engineering student, you probably think you have a good idea of 
what engineering is all about. I recall my goals when I entered engineer- 
ing school in 1971. It was all so clear then. High school students with an 
aptitude for math and science were destined to become engineers, and I 
was one of them. Four years of college would be followed by a secure 
career in the Engineering Lab, designing circuits that would change the 
world. I worked a few summers as a Technician, and I knew what engi- 
neers did. They designed circuits, gave hand-drawn schematics to the 
drafting department to make them nice and neat, then had the Technician 
round up the parts and build a prototype. Then the Engineer would come 
back to the lab and test the prototype, and blame any shortcomings on the 
lousy job the Technician did building the prototype. After a few itera- 
tions, the prototype would be declared a success, the Engineer would 
disappear for a few days to do something in his office, then come back 
with a hand- sketched schematic of the next circuit. And life went on. 

Then I graduated and became an Engineer. 1975 was not a good year 
to become an Engineer. Defense contractors had fallen on hard times, 
with the Vietnam War winding down. They weren't hiring Engineers. The 
economy was in tough shape, and the industrial companies were also 
hurting. Many of my fellow new Engineers were scrambling to get into a 
graduate school to hide until the job market got better. I was one of the 



197 



Analog Circuit Design for Fun and Profit 



lucky few that actually found a job — mostly because I had worked part- 
time as a Technician to pay for school, and I therefore had '*experieiicer 
Just getting an interview in 1975 wasn't easy. In fact, I had alreitfly been 
out of school for over a month when I got a call from the university's 
placement office to tell me that a company had reviewed the graduating 
class's resum6 book, and had invited me for an interview. My resum6 
touted some knowledge of both analog and digital circuits, and I claimed 
I knew which end of the soldering iron to hold. I could cobble a collec- 
tion of TTL gates together to do something, and could design a circuit 
with an op amp in it. I even had some experience in using and testing 
analog-to-digital converters. Fortunately, these were important things 
for this position, since my grade-point average was nothing special 
(too many extra-curricular activities . , .)A got the job. 

Then I found out what Engineering was really like. 

The first day on the job, my boss handed me the manual for the then- 
new Intel 8080 microprocessor, and told me to read it. Every day for the 
first week, he'd come into my office (actually, our office — four of lis 
shared the same office) and ask me how I was doing. He was a pretty 
good engineer and teacher, and I got the chance to ask him some ques- 
tions about things I hadn't quite understood. It went well. 

Then one day, he handed me a schematic of the 8080-based system he 
had just finished testing. This was my chance to see how he had designed 
the system's bus structure, and implemented the various sub-systems and 
their interfaces to the processor. It was mostly pretty straightforward 
stuff — all digital at this point. Then a few weeks later he came into my 
office and asked me to design an analog I/O interface for the system, 
including the signal conditioning, A/D and D/A conversion, logic inter- 
face, and various other pieces. This was the moment of truth — I was on 
my own for my first design. 

I had a handful of specs for the instrument we were supposed to inter- 
face with — voltage levels, source impedances, bandwidths, etc. I had the 
specs of accuracy of the original system. I had the manufacturers' data 
sheets for every component imaginable. And a week or so later, I had a 
design done — one of those hand-drawn schematics I had worked from 
as a Technician, but now I was calling the shots! Then we reviewed the 
schematic — the boss told me he had forgotten to mention that we needed 
to be galvanically isolated from the instrument we were hooking into. No 
problem; I had used V/F conversicai for the A/D, and a few opto-isolators 
later I had completed the revised design, including isolation, wdhc 
signed it off. I proudly marched into the lab, handed it to the Technician, 
and he saluted smartly on his way to build a prototype. 

Then a funny thing happened. The design part stof^ed for a long time. 
There was some haggling about certain parts being no longer available. 
The purchasing guy complained that some of them were sole-source, and 
he wanted everything to be multi-sourced. So I spent some time redesign- 
ing; the basic idea stayed the same, but the schematic was revised time 



198 



and time again to comply with everyone's needs. Then the software guy 
came over from the next office. He wanted a complete map of each I/O 
address, a description of each fimction, and the timing pauses required 
between operations. No problem — I wrote it all up for him over the next 
week or so, in between interruptions from the Tech and the purchasing 
guy. We met again to review what I had done, and the software guy re- 
minded me that the last project had included some provisions for calibra- 
tion and self-test. Back to the schematic — I added the required additional 
channels and test modes, and was finally done. The prototype had grown 
somewhat, and I was amazed that the Tech was still speaking to me (he'd 
seen all this before). 

Then the boss came in and asked me to document the operation of the 
circuit, including a description of every component's function. The pur- 
chasing guy came in with the manufacturing guy and they asked me for 
a complete parts list and bill of materials, and to sign off the final sche- 
matic. After a few iterations, everything was signed off, and the product 
went into production. I was eager to get to the next project. 

Then it got interesting. The main processor board that my boss had 
designed developed reliability problems — it was an obvious bug in the 
clock circuit, which I found by putting my finger on the pull-up resistor 
for the +12V clock. Half- watt resistors get hot when dissipating a whole 
watt. I got to fix that one. The analog input section worked fine when we 
used one manufacturer's V/F converter, but was noisy when we substi- 
tuted an "equivalent" from another manufacturer. I tracked the problem 
down to a difference in the power-supply decoupling needs of the two, 
and conjured up a scheme that was suitable for both versions. 

As production started, I was often called to determine if a component 
substitution was possible because one or more parts was temporarily out 
of stock. In some cases, the substitution had already been done, and I had 
to ftgiTO out why it didn't work. 

A ftill six months later, my boss asked me to design another circuit. 
Think about it — almost a half year between designs. Life as an Engineer 
was turning out to be very different from what I had expected. At least I 
was getting paid. 

When I was actually designing circuits, I discovered an assortment of 
interesting processes at work. There is recall — remembering previous 
circuits that may help solve the problem at hand. There is invention- 
defining the problem, and creating a new solution for it. There is experi- 
mentation — often, a difficult problem will require numerous tries to get 
to the right solution. In some cases, these processes are aided by various 
embodiments of design tools, from decade boxes to advanced state-of- 
the-art expert-system-based software. Lots of tools are available to help 
the designer create a solution to a problem. And each idea is weighed 
carefully, using all necessary processes and tools, against an endless pa- 
rade of design trade-offs, to improve reliability, increase production 
yield, and lower costs while maintaining or improving performance. 



Analog Circuit Design for Fun and Profit 



But it never ends at the design phase. After a circuit is done, and the 
first units are reduced to physical hardware, it reniains to determine if the 
thing actually solves the problem it was intended to solve. Testing, de- 
bugging, characterizing, and (often) doing it all again are part and parcel 
of the product development process. And lots of other authors have de- 
scribed their personal versions of this process in their chaptei^. 

I occasionally design circuits at home for recreation. Most are not the 
same as the kind of circuits produced by my employer, but my engineer- 
ing training and avocational interest in electronics motivate me to keep 
designing circuits from time to time. Nobody will ever buy tbem. Total 
production volume is usually one. And I get a real thrill when I see one 
of them work for the first time. And any engineer who has never felt the 
thrill of seeing his first units work perfectly first time out will probably 
not stay an engineer very long. In fact, the experienced engineer should 
feel the same sense of excitement when '*it works." Often, circuits don't 
work the first time. After an appropriate period (hopefully a short one!) 
of self-flagellation, the analysis of the circuit and troubleshooting begins, 
usually revealing an oversight or similarly simple error. The joy of find- 
ing the error usually makes the eventual event of a working circuit anti- 
climactic. And building circuits at home — with no formal documentation 
or parts lists required — ^the experience is as near to pure engineering as it 
ever gets. When I design circuits for myself, I define, design, build, test, 
redesign, rebuild, and use them. Unfortunately, it doesn't work that way 
in the real world. Most of the time, someone else is tdling you what to 
design. And someone else is building and testing "your" circuits. Yet 
someone else may redesign them. And most importantly, someone else 
is using your circuit, and has probably paid money to do so. 

A design engineer should never lose sight of the fact that his continued 
gainful employment is dependent on producing circuit designs that solve 
a problem for which his employer will collect revenue. Circuit design for 
fun is best left to the home laboratory, for those engii^rs who still have 
one. Circuit design for profit is serious stuff. If you can combine the two, 
consider yourself lucky. Then find a second spare-time leisure pursuit 
having nothing to do with engineering. 

I don't design circuits for a living any more. I moved frcnn Engineer- 
ing into Marketing (by way of a few years in Applications Engineering) 
some years back, but stayed in the electronics industry. While some mar- 
keting skills are easily transportable across industries (especially in pro- 
motion and merchandising), the product-definition part of marketing 
generally is most successful if the practitioner is close to the technology. 
I have had occasion to recmit marketing engineers from the technical 
ranks of our customers as well as the design and product engineering 
areas of our own company. Most have done well, but all have expressed 
great surprise at the amount of work involved in the job, compared to 
their previous lives in engineering (and most of them thought marketing 
was going to be easier!). 



200 



DougGrant 



DONL MOTHIMG OM W 
PK01"eCT. YOU 7U5T 
nCtP 5^YING 1 KAVENT 
GIVEN YOU SUPFXCIENT 




1 DOMT KNOU LJHAT 

ELSE YOU NEED AND 
YOU UON'T TELL ME 
UKAT YOU NEED!! 

i5Tni5 irU5r YOUR way 

OF AVOIDING LjOKK^f^! 




IIL BET YOU RIGRET 

CHOOSING nARI^eTING 
A5 A CAREER PATH. 

tT LOOKS LI^^ 
A LOr OF UWf 




DILBERT reprinted by permission of UFS, Inc. 



Steps in the Product Development Process 



The following steps broadly outline the product development process. In 
all cases, the *'you'* refers to yourself and your colleagues in whatever 
enterprise employs you. Product development is seldom a single-person 
endeavor. 

1. Concept — ^Find a problem that you think you can solve. 

2. Feasibility — Can you really solve the problem? 

3. Realization — Design and build the product. 

4. Introduction — Getting the product to the customers you don't 
know, 

5. Closure — Move on to the next problem. 



Step 1. Co?icept--Find a ProblemThat You Think You Can Solve 

A product is (obviously) something that is meant to be produced (manu- 
factured, delivered to someone for use, sold, consumed; take your pick). 
The point is that in the present era, very few circuits are designed for 
recreation only, Hardware circuit hackers are still out there, including the 
radio amateurs, but the fact is that most circuits are designed by engi- 
neers toiling for an employer. And that employer has an obUgation to 
its customers and shareholders to create things that solve its customers* 
problems, and in so doing, generate a profit. Oftentimes, these solutions 
take the form of innovative circuits, processes, or architectures. However, 
there is a weak correlation between commercial success and technical 
elegance or sophistication. 

A product must deliver benefit to the customer; it must solve his prob- 
lem. A circuit can be a part of a product, but it is never the product. A user 
needs to see some benefit to using your circuit over another. I recall re- 
viewing one particular product proposal from a design engineer that de- 
tailed a novel approach to performing analog-to-digital conversion. It 
seemed clever enough, but as I read it, the performance claims were no 
better than what existed on the market akeady. A cost analysis indicated 



Analog Circuit Design for Fun and Profit 



no improvement in cost over what existed already. Power wasn't better 
No particular features seemed to be obvious — it was just another A/D 
converter. I just didn't see any great benefit to a customer. So I called the 
designer and asked him what I had missed. He replied that the architecture 
was novel and innovative, and there was nothing like it. We reviewed the 
performance he thought he could get, and a chip size estimate. After about 
fifteen minutes, I asked him to compare the proposed chip to another we 
already had in development. There wasn*t any advantage obvious. Then 
I asked him to compare it to various academic papers. He replied that his 
architecture was more "creative*' than various proposed schemes. But 
when I asked him to show me where this idea would lead (higher speed, 
more resolution, lower cost, added features, scalability, user features, etc.), 
he drew a complete blank. Even assuming device scaling or proc^ add- 
ons, he (and I) couldn't think of where this would lead, I tesked if the in- 
spiration had come from a particular application or customer problem. 
The closest he could come was a personal-computer add-on card that he 
had seen once. He had no idea if the board was a big seller or not. 

The project was shelved. But I suspect that one day his novel ^irchitec- 
ture (or more likely, some part of it) will be useful in solving a very dif- 
ferent problem. 

I have also had the opportunity to deal with newly hired maiketing 
engineers. Their zeal for the perfect product often blinds them to reality, 
as noted in the comic strip. In defining specifications and features for a 
new product, there is the temptation to add every conceivable feature that 
any customer has ever asked for during the process of fielding requests 
from salespeople and customers. This leads to the frustration that engi- 
neers often have when dealing with marketeers. On the other hand, I have 
observed situations where the engineer has been unable to promise that a 
certain specification can be met, and a less-than-satisfying compromise 
was offered. Both parties need to spend some time analyzing which com- 
bination of features and specifications meets the requirements of the ma- 




ThE NEU PRODUCT 

TO DO. 




IT HAS TO HAVE A 

. INCH -i^KEEH 
AND STILL f IT IN 
A PURSE OR A 
WALLET. 



IT nU5T CURE DEADLY 
DISEASES AND 
WHITEN YOUR TEETH 
WHILE YOU sue P' 




HA HA ! ) AND IT HAS 
TO BE CAPABLE OF 
TlfAEl TRAVEL 1! AND 
HAVE A TELEPATHIC USER 
INTERFACE' 





f IT NittD^ ro ACT AS 

j ^ connuriiCAT\oN5 

■ ^ATELLUE A^i UlELL 
AS A ROOn FRESH- / 

. tNEK , , . ^ 




I COULD URITE A 
PROtKAn TnAT riAKEb 

Fish AppE^ ON rnt 

COfAPUTER SCREEN 




, YEAH A LOT OF ^ 
PEOPLE UJA^^ 




DILBERT reprinted by permission of UFS, Inc. 



202 



jority of the customers, and settle on these. "Creeping featurism" must be 
avoided, even if a customer calls just a vi^eek before design completion 
asking for one more feature, or if the designer discovers "a neat trick 
that could double the speed" at the last minute. Stick to the script! 
Last-minute changes usually result in future problems. 

As difficult as it may be designing high-performance analog circuits, 
it's equally challenging to figure out what to design in the first place. A 
wonderful circuit that nobody buys is not a good product. A rather pedes- 
trian circuit that a lot of people buy is a much better product. This is a 
tough concept for most of us to swallow, but it's the tmth. 

Making sure you understand the problem you are solving is probably 
harder than designing the circuit. You have to learn someone else's job 
and understand his problems if you are going to have any chance of solv- 
ing them. Numerous techniques have evolved over the years. One very 
effective methodology currently in vogue is called "Voice of the Cus- 
tomer," or "VOC" for short. The entire VOC process is lengthy and in- 
volved, and will not be described fully here, except for the first steps, 
which involve customer interviewing. 

I recall taking an IC designer to visit a customer in the video business. 
The designer had some ideas for a new AfD converter fast enough to digi- 
tize a video signal. A/D converters are generally described by their reso- 
lution (measured in bits) and speed (measured in conversions per second). 
We talked to the customer about his whole signal chain, from input con- 
nector to digital bus, to get a feel for the components he had used in his 
previous design. The A/D converter was an 8-bit part, with a certain con- 
version speed. As we talked, the customer began to complain that he 
couldn't get the resolution he wanted from the digitized image. Aha! We 
had discovered the problem to be solved. He needed more resolution! 

I glanced at the IC designer's notes and he had definitely gotten the 
point— he had written "RESOLUTION" in big letters, underlined, and 
circled it. Then he scribbled next to it: "Only has 8 bits now — 10 should 
be enough." Unfortunately, there is another kind of **resolution" in video; 
it refers to the number of pixels on the screen, and when a video engineer 
talks about resolution, he means the speed of the converter, not the num- 
ber of bits! Having done a fair amount of reading in preparation for the 
visit, I picked up on the error and asked the customer for a clarification. It 
went something like, "How much resolution do you need, and what does 
that mean in terms of the A/D converter?" His response was ultimately in 
speed terms and we got the discussion back on track (I knew it was back 
on track when the IC guy wrote "RESOLUTION = SPEED!!!?!" in his 
notebook). It is important to understand your customer's business and 
language before you go on the interview. 

Another time, I listened to a customer complain bitterly about an A/D 
converter that he claimed was outside its accuracy specs. I offered to test 
the device for him to verify its performance. When I tested the part, it 
was fine, meeting all specs on the data sheet. When I returned the unit to 
the customer, he insisted on demonstrating to me exactly how bad the 



Analog Circuit Design for Fun and Profit 



accuracy of the converter was. I went with him into his lab, where he put 
the converter in the socket, and turned the system on. He then tested the 
system by applying a dc signal from a bench power supply to the input 
and displayed the digital output on a monitor. He didn't even measure the 
DC input — just made sure it was somewhere within the AID converter's 
range, based on the reading on the front panel meter on the supply. Be- 
fore I could ask how he intended to verify 12-bit accuracy with a known 
reference source, he showed me that the output code was very unstable, 
with several codes of flicker evident. This was obviously the problem — 
noise, not accuracy! We tried all the usual cures (changing the supply to 
the converter from a switcher to a linear, rerouting the grounds a bit, and 
adding decoupling capacitors where there hadn't been any), and each 
change helped. Finally, we had the output stable. A fixed input gave a 
steady output value, even though we hadn't checked the actual accuracy 
of the system (he actually had no suitable equipment for such a test any- 
way). But he was happy — his problem was solved. We were happy — we 
got the order. 

The data sheet for our next A/D converter included detailed instructions 
on how many capacitors to use and where to locate them in the layout. It 
wasn't any more accurate a converter, but a lot fewer people complained 
about its **accuracy." And we added some tutorial information defining the 
various performance parameters of A/D converters, so the next customer 
who called complaining about accuracy would actually mean accuracy, 
and we would be able to diagnose and cure the problem faster. 

Speaking the customer's language is critical to communicating with 
him. And by "language" I mean his own company jargon or slang. If you 
expect him to learn your terms, you'll find it a lot harder to get him to 
feel comfortable describing the problem he wants you to solve. And this 
advice applies to both engineers and marketeers attempting to interview 
customers. 

The VOC process suggests working with a number of customers to 
collect images that allow you to understand their problem as they see it. 
This is important — satisfying the customers' needs in a way that they can 



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DILBERT reprinted by permission of UFS, Inc. 



204 



understand is the secret to success. The next step after collecting images 
of the customer' s-eye view of the problem is to re-state the problem in 
your own language so you can figure out a solution. All engineers should 
spend time with customers when they are in the process of discovering a 
problem to solve. Too often, a visit to a customer takes the form of trying 
to find a problem that fits your own creative solution. This violates all 
known problem-solving principles, but we all do it anyway. The obvious 
thing to keep in mind is that solutions only exist to solve problems; with- 
out a defined problem, it is only by sheer luck that a proposed solution 
does the job. 

Somt solutions are obvious — make it faster, more accurate, cheaper, 
lower power — ^but other problems exist that can be solved without the 
breakthrough innovations often needed to improve one of the conven- 
tional dimensions. TTiese can only be discovered by talking to customers 
and analyzing the data in a meaningful way to reveal what features or 
qualities of a product the customer will value. But remember—customers 
are in a different business than you are. It is up to you to make the effort 
to learn the customer's business and language in order to actually under- 
stand the problem and offer a solution! 

Interviewing a prospective customer involves some preparation. You 
should have a reasonable list of questions you want to ask, and you 
should be prepared to skip around the list as the conversation wanders. 
I have found it extremely useful to conduct interviews in teams of two. 
One person asks the questions, while the other scribbles the answers as 
fast as possible, trying to get it all down as nearly verbatim as possible. 
It's important to avoid adding too much commentary or analysis here — 
there's plenty of time for that later. Just get the facts down. If a series of 
questions has been missed, the note-taker can steer the conversation back 
to the areas missed. When I have tried to do customer interviews solo, I 
have often reviewed my notes only to find phrases like "He says the 
biggest problem is" or "The preferred package is," where I've been un- 
able to get it on paper fast enough, and the conversation has taken a turn 
to another topic too quickly. A second pair of ears and hands can help 
immensely. 

After the interview (which should end when the customer signals to 
you that he's done, not when you think time is up or have another ap- 
pointment), the interview team should compare notes and make sure that 
both have heard the same things. It is useful to re-construct the entire 
interview as it occurred to help the recall process. Clean up the notes as 
soon as possible so they can be shared and reviewed later in the process. 

After you've collected several interviews, the process of analyzing the 
data can begin. There is a strong temptation to give more weight to the 
last inputs you've received, unless you've taken the tinxe to get them all 
in readable forni. There is also a temptation to downplay inputs that con- 
tradict your own basic assumptions. Don't do it! Always remember that 
your product will be more successful if it solves the customer's problem 
than if it fits your personal model of the way things should be. 



Analog CirGuit Design for Fun and Profit 

The process used for analysis of the raw inputs can be complicated or 
simple. The underlying principle is always to get a customer's-eye view 
of what is important, and respond to it in a product definition. Conm^n- 
tary like, "They all say they want power consumption less than 50 milli- 
watts. That's ridiculous— there's a 10-horsepower motor in the system! 
Besides, my circuit topology takes that much just to power up the output 
driver" is to be avoided. Things that appear from your own perspective to 
be obvious contradictions like this need to be reviewed and understood, 
not dismissed. In the case just mentioned, you may discover thai the cir- 
cuit you are designing is used by the thousands in the system, and that big 
motor is only used to move the system into position, and powered exter- 
nally. The constraint on power is probably quite real. And you should 
figure out how important your output driver really is in his system. 

Step 2. Feasibil>ty--Can You Really Solve the Problem (and Is it 
Worth Solving)? 

This step follows whatever analysis tools you use to reveal the features 
and performance requirements of the solution you are planning. VOC, 
QFD, and other methods can be used, but none is a substitute for experi- 
ence, judgment, and general knowledge. At this point in the process, you 
should feel that you understand the requirements of the customers, and 
the first-cut solution is probably getting clear in your mind. In fact, you 
may think you have enough information to actually design a circuit at this 
point. Resist the temptation! You are in for some surprises. At this point, 
don't even try to complete the design — ^youTl find some feature you left 
out, or more likely, you'll have included a feature that only one customer 
(probably the last one you talked to!) wanted and which sounded like an 
interesting design challenge. Keep it sinq)le at this point. Don*t worry too 
much about the cost, or even the detailed architecture inside. Take a stab 
at the specs and features that seem important to the customer and difficult 
to meet, but don't waste too much time at this point. 

There are usually several alternatives to solving the customer's prob- 
lem. Usually the customer won't care much about the internal architec- 
ture, so you have a lot of freedom. You should get one pretty conservative 
solution defined quickly, then take some time to find alternatives that are 
better from the standpoint of cost, power, or ease in meeting some impor- 
tant specification for the customer. And feel free to think ''outside the 
box." 

This last expression comes from a course I once took on innovative 
problem-solving. A very simple puzzle is presented— draw three parallel 
rows of three dots each on a piece of paper; connect all nine dots by 
drawing four straight lines, never lifting the writing iinptement torn 
paper. The solution to the problem was an example of **going outside the 
box," as shown following. 

I had seen this puzzle before, and knew the trick, while others in the 
class were claiming it couldn't be done. I smugly told the tottsictor Fd 
be glad to show the others, since I knew the answer. Unfazed, he gave me 



206 



Going outeide the box. 

# • • 



• # # 

# # # 

the assignment of connpleting the puzzle by drawing only three Unes, 
This put me in the same bewildered predicament as the rest of the class. 
After several minutes of torture, the instructor revealed the solutions^ — 
using four lines, then three, two, and even one line! (Solutions appear at 
the end of this chapter. . . .) 

You should also talk to people that can provide assistance — other de- 
signers, applications or marketing engineers, anyone with some experi- 
ence. The chances are that a circuit to do something like this has been 
tried before. Remember the example of the A/D architecture without a 
home? Perhaps this is the right problem for that solution. Don't forget to 
check the literature. There's no sense in re-inventing the wheel— in fact, 
if someone else has a patent on that particular wheel, it could get expen- 
sive. And if you come up with an idea that looks original and has benefits 
over previous work, consider patenting it. 

If it turns out that the customer's problem does not have a solution that 
you can find that satisfies all the needs, there are a couple of options. One 
is to give up and move to the next problem. This is sometimes the best 
course of action. Some problems just don't have satisfactory solutions yet. 
File it away, keep in the back of your mind exactly what makes a solution 
impossible at this time, and keep your eyes open for the enabling technol- 
ogy. At that point, go back and see if the problem still needs a solution. 

If you can't find a way to meet all the required specs, try to meet as 
many as you can, and try the solution out on a few willing customers. It 
may turn out that solving three out of four is good enough. It may be 
three more than anyone else has proposed! 

Whether you think you're meeting some or all of the requirements, 
when you are closing in on the implementation, you must check to make 
sure you're still on course. Try describing your solution in terms of the 
customer's problem as you understand it. Survey methods can be used to 
rate individual features for importance, and "kill specs," or a series of 
loosely structured second-round interviews with willing customers, will 
work. When proposing a solution, be open to suggestions for improve- 
ment. This is not the time for defending "your" solution; after all, it isn't 
a solution yet — only an idea. If you are willing to make changes, cus- 
tomers will be willing to suggest them. And you'll find out quickly what 
is important that you missed, and what is superfluous. Pay attention, and 
bring someone with you again to take detailed notes for review soon after 
the visit. 



A. With four lines... 



Solution for 4 lines: 




Analog Circuit Design for Fun and Profit 



At some time, you will have to decide if this problem offers enough 
financial incentive for you and your colleagues to spend your time (and 
your employer's money) solving. This is the best time, before you invest 
a lot of time in the detailed design. I don't advocate a detailed market 
analysis that attempts to prove beyond a shadou^ of a doubt that this is the 
right thing to do. Instead, ask the customers if this is the right |Hroblem to 
solve. If they say no, figure out the right problem to solve* and solve that 
one instead. If you have your heart set on solving a particular problem, 
make sure somebody in your company solves this customer's most im- 
portant problem before someone in another company does it. 

You should go through the exercise of making sure the numbers add 
up. If you talk to ten customers in a certain end market, and they all claim 
30% market share, you have a problem. You may be able to get some data 
from an independent source to determine the actual shares (and thus the 
volume estimates for your solution), but often you v^ill have to rely on 
your own estimate. And determining which of these ten customers is likely 
to win in his market will be based on your own feelings about their relative 
competence as much as any market research you will be able to do. 

The failing of many product-definition processes, including VOC, is 
the myth that all customers are created equal, and that all customer inputs 
have equal weight. In many companies, a marketkig dep^ment or sales 
department determines which customers are the ones deser\qng of your 
attention. And despite the frequent culture clashes that occur among en- 
gineering, marketing, and sales, the truth is that all three organizations 
need each other. 

Some companies downplay the role of marketing in the product- 
definition process, while others recognize it for the valuable function that 
it can be. Even those companies that downplay its importance practice it 
religiously. One analog IC manufacturer has carefully chosen a group of 
customers it beUeves that it can profitably supply with circuits. It has 
then matched up a senior design engineer with each of these customers 
to learn what problems they are facing and try to figure out solutions 
together. Such client-based or partnership arrangements are becoming 
common in the industry, and represent one approach to the product defi- 
nition process. If you listen carefully to what your customer is saying, 
you should be able to figure out what you can do for him. But the practi- 
tioners of this marketing approach will often downplay the importance of 
the marketing role — after all, you just need engineers talking to engineers 
to figure out what to do next, and it will all work out, right? 

What these engineer-marketeers fail to realize is that someone picked 
out which customers they should get close to, and the marketing process 
began there, not at the product-definition step. 

Whoever chooses the target customers has to think long and hard 
about several things . First, which companies buy enough of the sort of 
products we make to justify a lot of attention? Second, which of these 
companies are in solid financial shape? After all, a customer without 
money to pay the bills is probably not a customer to pursue too aggres- 



208 



sively llird, which customers set the standard, or are considered by 
their paers to be market leaders? And finally, which ones do you want to 
bet on? Aad you need to keep reviewing these questions every couple of 
years^ because the answers to all the foregoing questions change over 

time. 

One of the classic mistakes in the customer-selection process involved 
a particular compoi^nt manufacturer (we'll call it "Company X," since 
this particular story has been handed down in the industry folklore for so 
long that the original company name has probably been long since lost) 
that chose not to extend credit to a start-up computer company started by 
two young engineers in a garage in Silicon Valley. That company grew to 
become giant Apple Computer, and certain key components in their prod- 
ucts are never supplied by Company X. 

Step 3. Realization— Design and Buiid the Product 

Assuming you have decided to move ahead and have the commitment of 
all the resources you need to get the project done, this is the part where 
you design the circuit and develop a product. Try several approaches. 
Don't force a known solution into this design if it doesn't fit. Also don't 
try to force an innovation where none is needed. Are you aiming for the 
Nobel Prize or a circuit that solves a customer's problem? 

The process of fine-tuning a design includes learning to tell the differ- 
ence between a good circuit and a bad circuit. In most instances, the 
difference is obvious. One works and meets specifications (including 
costs!), and the other does not. Case closed. But what about the case 
where both circuits meet spec? 

At this point, lots of questions need to be objectively answered (and 
some may not yet have objective answers!). Does one circuit have advan- 
tages in your manufacturing process? How about your customer's manu- 
facturing process? Does one circuit lend itself to further improvements as 
technology progresses? Does one circuit have a clear path that parallels 
the electronics industry's unrelenting goals of faster, cheaper, lower 
power, smaller, more efficient? Can someone copy it easily and rob you 
of the profits that are rightfully yours? And most important, will one en- 
able more profit over the long term than the other? This last one is that 
hardest to answer, and is left as an exercise for the reader. 

And it gets messier out there in the real world. Sometimes both de- 
signs "almost" meet spec. One meets everything except the speed, while 
the other meets every spec except the accuracy. Now what do you do? 

At this time, judgment separates the winners from the also-rans. This 
judgment must include conunon sense, experience of what has worked 
before and what has not, a real internal understanding of what the cus- 
tomer feels but is unable to express, and how the options compare with 
respect to all of this. Get opinions, facts, and make the call. 

I won't comment too much on the actual circuit design process here. 
Skip to another chapter for details on how to design analog circuits. 
HowcEver, there is one design-related topic overlooked by many of the 



Analog Circuit Design for Fun and Profit 



chapter authors in this series. It has little to do with circuit success, but 
everything to do with product success. It is the schedule, every engineer's 
enemy. 

When you know what the customer needs, you will also probably need 
to know when he needs it. This should have a major impact on the design 
approach you use. The first volume of this series suggested that in the 
case of designing a new IC, there are risks involved in new designs, new 
processes, and new packages. If you are designing to a tight schedule, 
you should probably not try to invent anything new. The more risks you 
take, the more likely it becomes that you will miss your customer's 
schedule. And if you miss his schedule, he will miss the sch^iute that 
his customer has given him. This means that everyone loses money. 

Occasionally people in sales or marketing will make a promise to a 
customer relating to a schedule without consulting engineering. They 
are trying to keep the customer interested, and figure that if they get 
the order, they can apply enough management pressure to make the 
product-development process move faster than usuad. I have also ob- 
served engineers making schedule commitments to customers that 
can't possibly be met (*'0h, yeah ... I can get the new design done in 
a week or two ... no problem"), ignoring the fact that the design phase 
of a product is usually not the most time-consuming part of the develop- 
ment process. One-sided commitments to customers will be a problem as 
long as enthusiasm and emotion get in the way of rational decision- 
making. Aside from increasing enrollment in karate classes, nobody wins. 



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It is also a good idea to qualify your customer by asking who his cus- 
tomers are. If there isn't a good answer, perhaps this isn't the right cus- 
tomer. Remember, a customer is someone who buys products from you 
and sends you money, not just someone who likes your ideas and thinks 
he might buy something someday. The latter is more of a prospect than a 
customer. I've been told that if you can't write down the phone numbers 
of three people who will buy your product, then you don't have a prod- 
uct. You should try this exercise on your customer, too. If your customer 



210 



has customers, try to talk to them. If you find out that all your customer's 
customers are planning to evaluate the new products at a particular indus- 
try event or trade show, you had better make sure that you have samples 
to your customer well in advance of the trade show so that he can assem- 
ble some prototypes to demonstrate. If he can't show units to his cus- 
tomers, both you and your customer may have to wait a year for the next 
show to launch a product. 

While it sounds cold-hearted to focus only on customers, prospects are 
important, too. Never forget that. You should be responsive, courteous, 
and provide the support they need, and even a bit more. However, most 
prospects understand their place in the Grand Scheme of Things. Most 
of them will realize that their potential business may not represent your 
highest priority, and some will also become suspicious if you spend a lot 
of effort on their limited potential. 

During the definition phase of a multi-channel D/A converter some 
years ago, I had determined that one potential market was numerically 
controlled machine tools and robots, since D/A converters are often used 
in position-control servomechanisms. Multi-axis motion controllers 
clearly needed multiple-channel D/A converters. I hit the books to find 
out the biggest manufacturers of machine tools and robots, and arranged 
a tour of them, focusing mostly on companies that were ahready cus- 
tomers of ours. The first few visits uncovered the sort of potential I had 
expected— on the order of a few hundred to a few thousand units each, 
with solid growth predicted for the next few years. Then I visited one 
company which was similar in size to the others (measured in annual 
sales), but which hadn't bought many chips from us in the previous year. 
In fact, they had only purchased small quantities of quite a few device 
types from us. This was puzzling, since they were housed in a very large 
building and had revenues comparable to the other companies. I pre- 
sented the idea for the new product we were defining to the engineering 
staff. They listened attentively, made a few suggestions on certain specs 
that were important to them, and requested a few features. As I noted 
these inputs, I asked what their production volume was for the next year. 
They looked at each other, and after some discussion, determined that 
their production for the next year would be between 10 and 15 machines. 
I asked if they meant per week or per month, and they explained that the 
machines they made were very specialized, and sold into a price-insensi- 
tive market. Their production volume of 10 to 15 machines per year rep- 
resteted the same dollar volume as some of the other companies we had 
interviewed, since these machines were very big (which explained the 
huge building) and very expensive. They were grateful for the attention 
we had given them, and were happy to help us. They were also a bit sur- 
prised that we had chosen them as a target customer. However, their sug- 
gestions turned out to be useful in the product definition, and became 
strong selling points when we went back to the larger-volume customers. 

By the time you have the first units, there are probably people waiting 
to try them. Some are inside your company (especially the people who 



Analog Circuit Desfgn for Fun and Profit 



have to manufacture the product in volume); some are outside your com- 
pany (customers). Presumably, there has been some effort expended to 
develop a way to evduate the first units to see if they meet spec. Do it 
quickly, and as soon as you are satisfied that the units behave as you ex- 
pect, get some in the hands of someone outside the company. Try to use 
someone who will tell other people if he lilces it, and tell only you if he 
doesn't like it. 

Very often, your interpretation of the customer's problem and his inter- 
pretation will still be different. The customer doesn't like your product. 
The reason is that you didn't meet the spec that was most impc^tant to 
him. Perhaps he didn't tell you clearly enough (or at all). Or else you 
didn't understand that it was so important. It doesn't matter where the 
fault lies — ^the customer is not happy because of a failuie to communicate. 
This is inevitable. If people always communicated clearly, th^ would 
have been far fewer wars in human history. Misunderstandings have cre- 
ated much more important problems than anything that may occur be- 
tween you and your customer (although it doesn't feel that way when it 
happens). Take a deep breath and try to work it out. 

Situations like this call for diplomacy and tact far beyond anything 
taught in engineering school, I have observed the tendency for engineers 
to get defensive when a customer finds a flaw in their circuit, especially if 
it has met the internally defined specifications. "I did my part. If it isn't 
good enough for the customer, that's his problem" is a fairly ridiculous 
statement if you think about it in the context of a supplier-customer rela- 
tionship. Similarly, the marketeer who says, "We did what they told us, 
now they should buy it," is also ignoring the obvious fact that he didn't 
really understand what the customer wanted. Remember — the customer 
has the final say. He has the money, and if you don't keep him happy, 
he'll send that money to someone else. If the product doesn't meet the 
critical spec, get back to work and fix it! 

Another problem I have observed is the case where a design works 
"sometimes." This is worse than a circuit that doesn't work at all Inter- 
mittent ability to dehver a product to a customer due to use of unqualified 
production processes, circuit blocks, packages, or whatever, will damage 
a customer relationship in more ways than you can imagine. In the old 
days, designers got one unit working, threw the finished documentation 
package over the wall to manufacturing, and went on to the next thing. 
That's not good enough. Manufacturing and Product Assurance must be 
routinely involved in the product-development process. They can offer 
valuable insight into mistakes that others have made, and help you avoid 
them. And while they may often ask lots of seemingly unrelated questions 
about a circuit during a design review, they are trying to help. 

But having discussed what can go wrong, it is equally important to 
mention that usually it all comes together right. You give samples to the 
customer on the date you promised, he tries them, and calls back to say 
how much he likes them. His system works exactly as he bad iK^ed, and 
he looks like a hero to his management. Then he shows his system to his 



customers and they like it. His customers place orders, then he places 
orders for your product. Everyone smiles a lot. 

Step 4. Introctactton— (Setting the Product to the Customers You 
Don't Know 

If it's a product, there must be a customer. And at this point in the process 
you protsably know some custon^rs already — some are probably calling 
you for updates on the progress of your product, because they have de- 
cided to use it even before they have seen any units. In fact, if you don't 
have a first-name relationship with at least three potential customers, you 
ought to reconsider the whole thing. Occasionally, you'll be so far ahead 
of their thinking that your product will be exactly what they want even 
though they don't know it yet. There are some cases where this has hap- 
pened — the personal compute, for example. But it happens so rarely that 
one of these per career is probably the limit. Without customers, you 
haven't designed a product — merely a circuit. 

Giving a few samples to a potential customer is one way to introduce a 
product to the market. It works when there are only a few customers for a 
very specialized product. It's possible to know most of them. It gets more 
difficult when there are more potential customers than you can handle 
personally. 

All customers will need help using your product. Some will need a 
little help, while others will need a lot of help. Still others will call you 
every day during the month they are designing a circuit around your prod- 
uct. Unless you have a lot of spare time available and need some new 
friends in your life, you have to create documentation adequate to allow 
them to use your marvelous widget without excessive hand-holding. 
Someone needs to write data sheets, instruction manuals, application 
notes, and troubleshooting guides. And that*s not all. Unless you are per- 
sonally going to be trained as a sales engineer, you will need to assume 
that other people with training in sales (yes, there is such a thing) will do 
the sellmg for you. If your product is going to be sold through a chain of 
distributors, you will need to provide sufficient training for them to under- 
stand your product's advantage over the competition (and how to handle 
situations where the competition is actually better in one respect or an- 
other). Unless you want every potential customer (or salesperson) to call 
you personally every time he has a question, you'll have to train other 
people to handle some of the questions in your place. This means time 
spent prep^ng and delivering trainmg materials. It's difficult to fit this 
in while you're designing circuits. 

Then there is the whole issue of external promotion to consider. There 
is a commonly held myth among both engineers and marketeers that de- 
rives from the "Build a better mousetrap and the world will beat a path to 
your door" axiom. It goes something like, *This product is so great it will 
sell itself.'* Too bad it isn't true. Here's what's wrong widi that idea. The 
term **better^' is completely subjective. If your customer hasn't been told 
why your product is better, he probably won't figure it out on his own. 



Amdcq Circuit Design for Fun and Profit 



He's probably too busy. You have to get tlie information to him somehow. 
Articles, seminars, trade shows, technical papers, newsletters — all of 
these are vehicles to get the information in front of the pcrteiHial buyers' 
eyes. And all of these need careful planning and execution to optimize the 
return for each dollar spent. And of course, someone has to do the work. 

Advertising is not as simple as it looks. A successful advisement 
appears in the media that are read by the target customers, as determined 
both by examining the publishers' audit statements and observing what is 
on the desk of the customers you interview. Perhaps direct mail is a better 
choice. Perhaps your company has a complete suite of conq)oiieats for 
this problem— a "family" promotion of some kind may be in order There 
are numerous vehicles available for product promotion — knowing them 
and choosing the most effective ones is the realm of the marketeer. 

The goal of product promotion is to g^erate leads, or names of people 
who are interested in possibly buying your product. There are other 
forms of promotion, of course, aimed at establishing or enhancing a com- 
pany's image so that the product promotions will remain effective. But 
promotion does not automatically result in revenue. Poorly planned and 
executed promotion plans only waste money. But an effective promotion 
plan can work wonders. 

Even if your product is demonstrably better, the customer ne^s to 
know where the "door" to your company is located. Who does he call if 
he wants to buy the product? Does he know who your company is? Do 
the other people in his company know how to do business with y<mr 
company? And lastly, if the manufacturer of the second- or even third- 
best mousetrap has a sales force that beats a path to your potential cus- 
tomers' doors, the world will have no reason to beat a path to your door, 
and you will not succeed. Having the world's best product simply isn't 
enough. 

Yes, you need salespeople. Most engineers do not like salespeople. 
Many engineers consider circuit design a Higher Calling of sonte sort, 
and have little interest in the human interactions that enable the exchange 
of goods and services in a market economy. However, without these in- 
teractions, little commerce could take place. 

Being on the losing end of a potentid order due to a lack of relMion- 
ship is frustrating. I recall one incident where after investing many months 
of effort, including several long-haul airplane flights, we lost a very big 
order at Customer A to Competitor X. I knew our product was better. I 
knew our price was better. I knew the overall solution cost was better. The 
overall system performance with our product was better. Yet we lost the 
order. We were all at a loss to understand why we lost the order. We had 
done everything right, by any measure. It took a while, but finMly one of 
the Customer A designers told me what had happened. The order we were 
seeking was even more important to Competitor X than it was to us. The 
sales manager of X raised visibiUty of the impending lost business to the 
president of the company. The Competitor X president then phoned his 
old friend who was president of Custon^r A, and made an appointment to 



214 



Doug Grant 



play golf the next weekend. Somewhere on the back nine, the issue of the 
new project was raised, and Mr. X asked his old friend if there was any 
way to use his company's product in the new project. He had heard some 
disturbing things about possibly losing the order. The next day, Mr. A 
called his engineering and purchasing managers and instructed them to 
use the Competitor X product. They saluted smartly, and followed orders. 
In this case (and there have been numerous others over the years) the 
human relationship outweighed the objective and fact-based decision- 
making processes. Losing business this way is frustrating. Getting to the 
point where you can win this way takes a long time, a soHd track record of 
success^ and a good sales force. 

It is worth noting that most salespeople have a pretty low opinion of 
engineers as well. They see most engineers as unable to see the obvi- 
ous importance of their customer, and can*t understand why it's hard 
to improve the performance of a circuit by a mere factor of two by 
just making a minor adjustment that should take no time and entail 
no risk. 




After introduction, someone must consider the management of the 
life-cycle of the product. Periodically reviewing the performance of a 
product against measurable data (sales, profits, units sold, etc.) is a neces- 
sary evil, and generally unrelated to circuit design. Long after a product 
has been introduced, someone (variously called a product manager, mar- 
keting engineer, or merchandising specialist, depending on the company*s 
culture) reviews all these (and other) metrics, analyzes the cause, and 
undertakes corrective actions as necessary. If sales have declined, it may 
be that price has eroded due to new competition, a major program has 
ended, or some other phenomenon. It is unlikely that the manufacturing 
or accounting operations of your company will have visibility into the 
end customers, and they can only build product and report data. Someone 
who can examine the data and determine which course of action leads to 
the maximum revenue and profits must make the decisions regarding the 
product. 



Analog Circuit Design for Fun and Profit 



Of course, you may want to do much of this yourself. And that's fine, 
as long as you recognize that you will have less and less time available 
to design circuits. Or to learn about other kinds of circuits and systems. 
Consider such a decision very carefully. 

Step 5. Closure^ove On 10 tftt 

While it is important to deliver circuit designs that meet certain specifica- 
tions, it is not advisable to succeed once, and then rely on incremental 
improvements on the same idea from time to time for the rest of a career 
Once you have completed the process of solving a customer's problem, 
it's time to declare victory and move on. Document what you did, make 
sure that the solution is on "autopilot," train others to understand the 
issues and trade-offs made, and then walk away. 

You need to do new things from time to time to avoid getting stale. In 
the area of circuit design, doing the same things the same old way and 
just waiting for incremental improvements (new processes or compo- 
nents) can type-cast an engineer and limit his professional growth. If 
that's your choice, make sure you understand its impHcations. Most engi- 
neers I have known have looked for new ways to do things, and often find 
old tricks useful in solving new problems. 

But where do you find new problems to solve? There are several 
sources of inspiration for what to do next. The best (and sadly, the most 
often overlooked) source of ideas for new products is your current cus- 
tomers. Remember the customer you designed a low-noise amplifier for 
last year? Perhaps he also needs a high-resolution AID converter. Or the 
guy who needed a battery monitor — ^he might need something else 
vaguely analog in nature. Talk to him. But do a bit of homework your- 
self—find out what projects your company already offers so you don't 
spend a lot of time identifying a problem that others in your company are 
already solving. As companies grow, it becomes difficult to know what is 
going on in other parts of the organization; this is another place where a 
salesperson can be useful. He is expected to know what products his 
company has available now and in development to solve some customer's 
problem. If he hears his own customer express a similar need, he can 
then bring in the resources he needs to find the best available solution for 
his customer's problem. 

I recall one visit to a customer where I had one of our design engi- 
neers with me. The customer was having a minor problem with one of 
our D/A converters, but had solved it by the time we got there. However, 
since he had the "factory guys" there, he wanted to tell us about another 
problem that he couldn't solve. Ever the eager marketing type, I asked 
him to tell me more^if my own group didn't have the solution, I could 
carry the message to the relevant group and get him the help he needed. 
The customer then launched into a lengthy dissertation on what was 
wrong with a particular class of IC that didn't work quite right — it was 
something that connected to a D/A converter, so I was curious. About 
five minutes into the interview, my colleague inteirupted the customer to 



2t6 



inform him that we didn't make that kind of device, and we couldn't help 
him. He didn't want the customer to waste his time explaining a problem 
we couldn't solve. 

As it happened, however, another part of our company was in fact in 
the final design stages of a chip that was very well suited to solving the 
customer's problem. I had to play the diplomat and remind my colleague 
about the device under "secret development " and encourage the customer 
to ^ ep talking. I took lots of notes, forwarded them to the appropriate 
group in my company, and we eventually did some very nice business 
with that customer. 

Engineers working in high technology need to keep abreast of the 
latest research in their field, including new technologies. Many analog 
circuit designers look with disdain upon digital design; however, there 
are powerful techniques available in the digital domain that have peifor- 
mance and cost advantages over any attempt to duplicate them in the 
analog domain. Knowing something about them can help broaden your 
range of available trade-offs. 

Read the journals; attend a conference or two each year, including one 
intended for your customers. Talk to people, especially others in your 
company who deal with a lot of customers. Buy things and take them 
apart to see how they work. Find out who is trying to solve similar prob- 
lems to yours, perhaps in a different end application. The ideas you en- 
counter may someday be useful. Learning is almost never in vain — an 
idea whose present worth is questionable sometimes becomes a solution 
to a problem in the ftjture. And solving problems profitably is quite satis- 
fying indeed. 

And here are the solutions to the "connect-the-dots" problem . . . 
**draw three parallel rows of three dots each on a piece of paper; connect 
all nine dots by drawing four straight lines, never lifting the writing im- 
plement from the paper." 



Analog Circuit Design for Fun and Profit 

With three Hnes 



Solution for 3 lines; 




C. With two . . , 



Solution for 2 tines: 




D. And finally, with one line . 

Solution for 1 line: 



Robert Reay 



1 3. A New Graduate's Guide to the 

Analog Interview 



It wasn't that long ago that armed with a couple of engineering degrees 
and a snappy new suit, I walked headlong into disaster: my first technical 
interview. The interview was with a well-known Silicon Valley integrated 
circuit manufacturer, and I had no idea what was in store for me. After 
flailing through six one-hour grueling technical sessions and my first 
power lunch, I remember stumbling to my car while visions of pn junc- 
tions, amplifiers, TTL gates, and flaming airplanes in a deadly tailspin 
swam though my brain. What went wrong? 

I didn't go into the interview unprepared. I attended the "how to inter- 
view" classes held by the career placement center. The center's staff had 
helped me create a resume with plenty of style and power adjectives. I 
was forced to watch the videotape of my practice interview in hopes that 
my awkward hand gestures and use of the deadly "you know" and "uh" 
might improve. My girlfriend (now my wife) had picked out the tie. I had 
five years of engineering classes and lab experience, and had spent the 
last two learning about analog IC design. I had torn apart my Apple II 
computer, designed and built my own stereo amplifier, and knew where 
the power-on button of a Tektronix 547 oscilloscope was located. 

What went wrong? The people in the career planning office had taught 
me about the generic interview, my professors had taught me about ana- 
log circuit design, but it was up to me to learn how to combine the two. It 
took a couple of days of "on the interview training," before I finally got 
the hang of it, and the interviews became easier. 

Now that I am sitting on the other side of the interviewing table, I find 
that most students still find themselves in the position I was in 10 years 
ago. The first interview is tough, and the last is easy. So here are some 
tips that I hope will make your first interview as good as your last. All it 
takes is a little preparation, knowing what to expect during the interview, 
and being able to solve a handful of basic analog circuit problems. 

Preparation 

Be prepared to answer this question intelligently: what do you want to 
do? It is surprising how many students fumble for answers when asked 
this question. I have actually heard students say "uh, graduate" and "get a 



219 



A New Graduate's Guide to the Analog Interview 

job." Wrong. A well-thought-out answer with a dash of enthusiasm will 
go a long way towards getting an offer letter. As an interviewer, I would 
like to hear something like^ "I want to join your cofflpany so I can sit at 
the feet of the gurus of analog integrated circuit design," but since this has 
yet to happen, I would settle for someone who says he has a keen interest 
in analog design and is willing to work hard» 

All good interviewers will ask you to describe something that you have 
done before, so learn one circuit or system very well. It could be from a 
senior project, classwork, a final exam, or simply a late-night home-brew 
circuit hack. Have your classmates or an advisor pepper you with ques- 
tions about the circuit. "What is the bandwidth? How did you compensate 
this node? What is the function of this transistor?" I like to ask the fol- 
lowing question during an interview: draw me the schematic of any am- 
plifier that you have designed and tell me about it. I then see how far the 
student can go in describing the circuit. The idea is to put the student at 
ease by having him describe a circuit that he is familiar with, while I find 
out how well he really understands the circuit. 

If you describe a design or research project on your resume, you better 
know it backward and forward. I occasionally interview a student whose 
resume claims he has worked on a very challenging project, but he is 
unable to answer even the most basic technical questions about it. Adcting 
a flashy project to your resume may get you noticed, but if you are not 
prepared to discuss the project's technical details in depth, it is the quick- 
est route to a rejection letter. If you don't thoroughly understand some- 
thing, leave it off the resume. 

Before you go to the interview, find out what the company does. Find 
a data book or other literature that describes the company's products. By 
becoming familiar with the product line, you will be able to anticipate 
what technical questions you will get, and be able to ask some mspired 
questions. For example, when a classmate of mine was about to interview 
at a satellite communications company, he spent an entire day in the 
Stanford library reading all of the IEEE journal articles that the com- 
pany's famous chief scientist had written. During the interview, my class- 
mate was asked how he would design a certain system, so he said, *'Well, 
at first glance I would probably do it like this . . . then went on to de- 
scribe everything he had read in the chief scientist's articles. Of course 
my classmate came out of the interview looking like a genius and got the 
offer. 

Know ahead of time what salary you want. Go to the career placement 
center and get a salary survey of students in your field with the same de- 
gree. It is best to know what you are worth so you can negotiate the salary 
you want in the beginning. Once you start working it is too late. 

Prepare a set of questions that you will ask the interviewer. What is the 
worst and best part of his job? How does he like the company? What is 
the most difficult circuit he has designed? Design some questions so you 
get a feel for what it is like to work at that company, and wheflier or not 
you will be able to work with these people 8+ hours a day. 



220 



Finally, keep in mind that most managers think that enthusiasm, will- 
ingness to woric hai^, good communication skills, and amiable demeanor 
are tnueh more importsmt than the ability to solve a handful of tricky cir- 
cuit problems. So ^«^n you iiUerview, relax. Try to convey your love for 
analog design, your willingness to work hard, and try to stay cool. And 
please, remember not to call the interviewer "dude." (That actually hap- 
pened more than once.) 

Most companies go through a three-step interview process. The first step 
is a quick on^caii^us interview to make sure that you are really in the 
electrical engineering program, you can speak in complete sentences, and 
you can answer some basic circuit questions. If you don't look like a 
complete bum, show an interest in analog design, and can recite Ohm's 
Law from mOT«3ry, you can usually make it past this interview. 

The second interview is over the phone with the hiring manager. He 
wants to make sure that is worth the time and effort to bring you into the 
plant for the final interview. The phone interview usually consists of ask- 
ing what classes you took, asking you to describe the project listed on the 
resume, then a series of simple circuit questions. 

The third and most important interview is at the factory. The hiring 
manager will generally warm you up with a cup of coffee, a plant tour, 
and a description of the work the group is doing. Then all hell breaks 
loose. You will have several one-hour technical interviews with different 
engineers, a lunch interview where the technical staff tries to determine 
your compatibility with the group while you bravely try to describe pn 
Junction theory and chew at the same time, followed by an afternoon of 
more technical interviews. If you have an advanced degree, you will usu- 
ally be required to give a lecture to the technical staff as well. 

TTie term '^technical interview" doesn't tell the whole story; "technical 
grilling" is more appropriate. After the usual introductions and discussion 
of your career goals, etc., the grilling will begin. If the interviewer is 
good, he will have you describe the circuit or system listed on your re- 
sum€, which you will ace because you came prepared. Then the inter- 
viewer will pull out his favorite technical questions. These are usually 
designed to test your basic knowledge of circuit design, and more impor- 
tantly, they allow the interviewer to evaluate your approach to solving 
problems that you have not seen before. 

Some interviewers will have you solve the problems on paper, others 
on a matker board on the wall, but in either case, you will be required to 
think on your feet. Remember that the interviewer is looking at your ap- 
proach to solving the problem and doesn't always expect you to solve it 
completely. When trying to solve a new problem, resist the temptation to 
start writing equations right away. Stop and think about what is really 



A New Graduate's Guide to the Analog Interview 

happening in the circuit. Try to reason out the function of different sec- 
tions of the circuit and decide what parts you do and don't understand. 
Try to describe out loud what you are thinking. For instance, "If this node 
goes up, then that node goes down, so the circuit is using negative feed- 
back." Once you understand how the circuit works, and you have a plan 
of attack, then you can pull out the equations. 

Remember that it is always much better to say that you don't under- 
stand something than to guess. You'll never get hired if a manager thinks 
you are trying to b.s. your way through a problem. Rather, tell the inter - 
viewer what you do know, and what you don't understand. Tell him what 
you will need to know in order to solve the problem. 

Try to jot down some notes about each question that you are asked. If 
you weren't able to solve it completely, try to finish it at home. You will 
be surprised at how many times the same circuit problem comes up at 
different interviews. When I was interviewing, I heard some questions so 
many times that I had to force myself to prevent the answer from sound- 
ing like a tape recording. (#1 question: What are the components of the 
threshold voltage for a MOS transistor?) 

Make sure that you get a list of the people that interviewed you and a 
business card from each one. It is always a good idea to write all the in- 
terviewers thank you notes a couple of days after the interview, as it pro- 
vides an easy way of reminding them of who you are and that you really 
want a job. Even if you don'tget a job offer, they may provide valuable 
contacts in the future. 

Sample Interview Questions 

Interview questions come in all shapes and forms. I had to complete a 10- 
page exam for one interview. The first problem was trivial and each one 
got progressively harder, with the last one being mind-numbing. The in- 
terviewer used the exam to keep track of how well each university was 
preparing its students, and as a reference to remember each student. 
(Results: #1 UC Berkeley) Some companies, like Hewlett-Packard, like to 
ask tough questions that are not related to your field of expertise just to 
watch you sweat. I had this question while interviewing for a circuit de- 
sign job: "You have a beaker of water with diameter x, water depth y, and 
you stir the water at a constant rotational velocity. How high does the 
water move up the sides of the beaker? FU give you any equation you 
need to know." But you* 11 find that most questions are simple and keep 
appearing over and over. Here is a sample of common interview questions 
that I have accumulated over the years from my friends in the analog 
business (yes, the answers are in the back): 



222 



Robert Reay 



Ql. If you put a O-to-5-voltstep voltage referenced to ground into the 
cireuits shown in Figures 13-1 A and 13-lB, sketch the wave 
forms you would expect to see at the outputs. 



5V 



ov 



o — vw 



o Vo 



=T= 



Figure 13-1. 




Q2, As the base emitter voltage of the bipolar transistor Ql in Figure 
13-2 is increased from OV, sketch the voltage at the output node. 




Figure 13-2. 



Q3, Two loudspeakers with a passive input filter are shown in 

Figures 13-3 A and 13-3B. Which one is the woofer, and which 
one is the tweeter? 



Ft^re13-3. 




223 



A (few Graduate's Guide to the Analog Interview 



Q4, In Figure 13-4, the diode and transistor are a matched pair. If the 
forward voltage of the diode is 0.7V, what is the approximate 
collector current in the transistor Ql? 



12V 



Rgure 13-4. 




Q5. A constant-currerit lo is fed into the diode coflnected-tmn^stor 
Ql shown in Figure 13-5. What happens to the output voltage Vo 
as temperature is increased? 



Figure 13-5. 



Vcc 



lo 



-oVo 



Ql 



Q6. The ideal op amps of Figures 13^ A and 13-6B are connescted 
with feedback resistors Rl and R2. What is the closed^toop IX::^^ 
gain of each configuration? 




Robert Reay 



Q7, Assume that the op amps of Figures 1 3-6A and 1 3-6B have 
finite gain A^. Now what is the closed-loop DC gain? 

Q8. The capacitor of Figure 13-7 is connected with two ideal MOS 
switches. Switches Tl and T2 are alternately turned on with a 
frequency f^. What is the average current flowing from node 1 to 
node 2? What is the equivalent impedance from node 1 to node 2? 




Q9, The regulator of Figure 13-8 has an input voltage of 8V, a bias 
resistor Ri of lOOQ, and 10mA flowing through the 6V zener 
diode. Calculate the value of beta of the NPN transistor Ql if the 
load current is 100mA, 



+8V^ 



TJ~h 



Ql 



100 

6V 
zener 



i 10 mA 



i 100mA 



Figure 



QIO, Assume that the diode Dl of Figure 1 3-9 is ideal. Sketch the 
wave form of Vo. 

Dl 



120 sin (ot 




10:1 
Turns Ratio 



Figure 13-9. 



225 



A ffew Graduate's Guide to the Analog Interview 



Qll. The bipolar transistor of Figure 13-10 is biased so the voltage 
across Rl is 260niV. A small AC signal is applied to the input 
node. Qualitatively describe what die voltage at the output looks 
like. Calculate the AC gain. 



Vcc 



Figure 13-10. 



Vin 




Q12. A two-pole amplifier is found to have an open-fee^ BC g^ of 
lOOdB, a gain-bandwidth product of lOMHz, and 45" of phase 
margin. Sketch the Bode plot for the open-loop amplifier, show- 
ing the gain, phase, and location of the poles. 

Q13. The Darlington pair of NPN transistors Q 1 and Q2 in Figure 
13-1 1 each have a current gain of p. What is the approximate 
total current gain of the pair? 



Figure 13-11. 



Vcc 



Rl 



R2 S 









Ql 





Q14. The dmin cuirent of the IFET shown in Rgure 13-12 is 2.5mA 
when Vgs is set to -2.5V; and 2.7mA when Vgs is -2.4¥. Calcu- 
late the pinch-off voltage and the drain-source saturation current. 



226 



Robert Reay 



Vcc 



Figure 13-12. 




Vgs 



O 



A CMOS amplifier consisting of PMOS device Ql and NMOS 
device Q2 is shown in Figure 13-13. Assuming that they both 
have the same gate oxide thickness, y/hat is the approximate gain 
of the amplifier? 



Q16. You are probing a square wave pulse in the lab that has a rise 
time of 5ns and a fall time of 2ns. What is the miniinum band- 
width of the oscilloscope needed to view the signal? 

Q17. What is the thermal rms noise voltage of a Ik resistor at 300K? 

QIS. A transistor dissipates 25 W in an ambient temperature of 25*^0. 

Given that the thermal resistance of the transistor is S'^CAV and 

the maximum junction temperature is 150*'C, what is the thermal 

resistance of the heat sink required? 
Q19. Draw the equivalent circuit of an exclusive-nor gate using only 

inverters, nand, and nor gates. (Hey, even analog guys need to 

know som^ digital stuff.) 

Q20» You are bifered the following jobs; which one do you take? 

a. Hacking C++ code for Windows 

b. A windsurf instructor at Club Med in the Canary Islands 

c. A roadie for the upcoming Rolling Stones tour 

d. An analog design engineer 



Vcc 




227 



A New Graduate's Guide to the Analog Interview 



FigiHre 13-14. 



Answers to Sample Interview Questions 

Ql. Remember that the voltage across a cs^acitor cannot cten^ instan- 
taneously, and the time constant is 1/RC, as shown in Figuie 13--14. 





B 



Q2. The output voltage has three distinct regions as sbowR inJFigure 
13-15: Ql off, Ql in the linear region, and Ql saturated. 



Figure 13-15. 



Vo 



+6V 



OV 



off 



.6V 



• linear 



saturated 



■VIn 



Q3. Assuming that the filter prevents high frequeiMjies from reaching 
the woofer; and low frequencies from reaching ftie twfeelen A is 
the woofer, and B is the tweeter 

Q4. Thecurrentthroughthediode = (12-0.7)/11.3k= 1mA. If the 
diode and Ql are a matched pair, then the circuit is a current 
mirror with the collector current equal to 1mA. 

Q5. With a constant collector current, the output voltage will show a 
slope of ~ -2 mVrC. 

Q6. Figure A has an inverting gain of -R2/R1 and B has a noninvert- 
inggainof (1 +R1/R2). 

Q7. Figure A has an mverting gain of l/( 1/Ao + Rl/Ao - B1/R2). 
Figure B has a noninverting gain of (R2 + R1)/[(R2 + Rl)/Ao 
+ R2]. 

m 



Robert Reay 



Q8. For every clock cycle, a small amount of charge = C(V1 - V2) is 
transfeixed to and from the capacitor. Therefore, the average 
current is i = q/time or i = Cf^CVl - V2), The equivalent imped- 
ance is AV/i = 1/Cf, 

Q9. The current in the resistor is (8 - 6)/100 = 20mA. If the zener 
requires 10mA to sustain 6V, then the base current of Q l is 
20mA - 10mA = 10mA. The transistor is then operating with a 
beta of (leAb - 1) = (lOOmA/lOmA - 1) = 9. 
QIO- With a 10: 1 turns ratio, the peak voltage on the secondary side of 
the transformer is 12V as shown in Figure 13-16. On the positive 
half cycle, the diode is not conducting so the output voltage is 
divided in half. On the negative half cycle, the ideal diode con- 
ducts so that the full voltage appears at V^. 




Figure 13-16. 



Qll. If the input voltage is a small-signal sine wave, then the output 
voltage is an amplified sine wave of opposite polarity. If the 
output impedance of Ql » RL, then the gain of the circuit is to 
first order the of Ql times the load resistance, A^ = - gm * Rl- 
With gm = IcA'^t the gain can be rewritten to Ao = -Ic ^J^v 
Recognizing that 1^ Rl = 260m V, the equation becomes Ao = 
-260mVAA, or Ao = -260mV/26mV = -10. 

Q12, The first pole = lOGHz, the second = lOMhz as shown in Figure 
13-17. 

Q13, Current gain = p (p + 1) 

Q14 Knowing that Id = loss ( 1 - set up simultaneous equa- 

tions and solve for Ipss = 9.8mA and Vp = -2.45V. 

Q15, The gain = (g„ n-channel/gn, p-channel). Since g^, = 2 (K72 * 
W/L * Id)*^ and the mobility of the N-ehannel is approximately 
3 times that of the P-channel and Id is the same for both transis- 
tors, the gain = (3 * I2y^/(9y^ = 12. 

m 



A ftew Graduate's Guide to the Analog Interview 



Figure 13-17. 



— ICDODb 




Q16. The time that it takes an RC circuit to go from 10% to 90% of its 
final value is At = ln9 * RC . If the b^didwidth of the 'sce^ SW^= 
VaTiRC, then the bandwidth BW = In 9I{2k * At) = ln9/(2jl: * 2ns) 
= 174MHz. Choose a 200MHz or faster 'scope. To reduce errors, 
choose a 'scope 3 times faster than the calculated value, or 
600MHz. 

Q17. The average noise voltage squared, = 4kTR Af, so V~ 

4nV/(Hz)^^. 

Q18. The required 8 ^ (150^ - 25°)/25 W = 5°AV. Since the package 
has a thermal resistance of 3°C/W, the heat sink mti$t Se a naihi- 
mum of 0 = (5*^CAV - 3^G/W) = 2°C/W. 

Q19. The equation for an exclusive-or gate is Y = ab' + ba*. Ttis can be 
rewritten as Y = [(ab*)' (ba')T. The logic diagram is shown in 
Figure 13-18. 

Q20. b 




NUMBER CORRECT RECOMMEND/mON 



1 -5 Become a bond trader. 

6-10 Buy a copy of Gray and Meyer. Memorize it. 

1 1-1 5 Not bad; call up National Semiconductor. 

16-19 You have a future as an analog engineer. 

20 Give me a call. I know a great boardsailing spot 

where we can sail and discuss job opportunities. 



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Lloyd Brown 



14. John Harrison's "Ticking Box"' 



There was never a shortage of inventive genius in England, and many 
fertile minds were directed towards the problem of finding longitude at 
sea. In 1687 two proposals were made by an unknown inventor which 
were novel, to say the least. He had discovered that a glass filled to the 
brim with water would run over at the instant of new and full moon, so 
that the longitude could be determined with precision at least twice a 
month. His second method was far superior to the first, he thought, and 
involved the use of a popular nostrum concocted by Sir Kenelm Digby 
called the "powder of sympathy." This miraculous healer cured open 
wounds of all kinds, but unlike ordinary and inferior brands of medicine, 
the powder of sympathy was applied, not to the wound but to the weapon 
that inflicted it. Digby used to describe how he made one of his patients 
jump sympathetically merely by putting a dressing he had taken from the 
patient's wound into a basin containing some of his curative powder. The 
inventor who suggested using Digby's powder as an aid to navigation 
proposed that before sailing every ship should be furnished with a 
wounded dog. A reliable observer on shore, equipped with a standard 
clock and a bandage from the dog's wound, would do the rest. Every 
hour, on the dot, he would immerse the dog's bandage in a solution of the 
powder of sympathy and the dog on shipboard would yelp the hour. 

Another serious proposal was made in 1714 by William Whiston, a 
clergyman, and Humphrey Ditton, a mathematician. These men suggested 
that a number of lightships be anchored in the principal shipping lanes at 
regular intervals across the Atlantic ocean. The lightships would fire at 
regular intervals a star shell timed to explode at 6440 feet. Sea captains 
could easily calculate their distance from the nearest lightship merely by 
timing the interval between the flash and the report. This system would be 
especially convenient in the North Atlantic, they pointed out, where the 
depth never exceeded 300 fathoms! For obvious reasons, the proposal of 
Whiston and Ditton was not carried out, but they started something. Their 
plan was published, and thanks to the publicity it received in various peri- 
odicals, a petition was submitted to Parliament on March 25, 1714, by 
"several Captains of Her Majesty's Ships, Merchants of London, and 



*Reprinted from *The Story of Maps" 



Jolm Harrison's 'Ttcking Box" 



Commanders of Merchantmen," setting forth the great importance of 
finding the longitude and praying that a public reward be offered for some 
practicable method of doing it. Not only the petition but the proposal of 
Whiston and Ditton were referred to a committee, who in turn consulted a 
number of eminent scientists including Newton and Halley. 

That same year Newton prepared a statement which he read to the 
committee. He said, "That, for determining the Longitude at Sea, there 
have been several Projects, true in the Theory, but difficult to execute." 
Newton did not favor the use of the eclipses of the satellites of Jupiter, 
and as for the scheme proposed by Whiston and Ditton, he pointed oat 
that it was rather a method of "keeping an Account of the Longitude at 
Sea, than for finding it, if at any time it should be lost." Among the meth- 
ods that are difficult to execute, he went on, "One is, by a Watch to keep 
time exactly: But, by reason of the Motion of a Ship, the Variation of 
Heat and Cold, Wet and Dry, and the Difference of Gravity in Different 
Latitudes, such a Watch hath not yet been made." That was the trouble: 
such a watch had not been made. 

The idea of transporting a timekeeper for the purpose of finding longi- 
tude was not new, and the futility of the scheme was just as old. To the 
ancients it was just a dream. When Gemma Frisius suggested it in 1530 
there were mechanical clocks, but they were a fairly new invoition, and 
crudely built, which made the idea improbable if not impossible. The idea 
of transporting "some true Horologie or Watch, apt to be carried in jour- 
neying, which by an Astrolabe is to be rectified . . " was again stated by 
Blundeville in 1622, but still there was no watch which was "true" in the 
sense of being accurate enough to use for determining longitude. If a 
timekeeper was the answer, it would have to be very accurate indeed. Ac- 
cording to Picard's value, a degree of longitude was equal to alK>ut sixty- 
eight miles at the equator, or four minutes by the clock. One minute of 
time meant seventeen miles — towards or away from danger. And if on a 
six weeks' voyage a navigator wanted to get his longitude within half a 
degree (thirty-four miles) the rate of his timekeeper must not gain or lose 
more than two minutes in forty-two days, or three seconds a day. 

Fortified by these calculations, which spelled the impossible, and the 
report of the committee. Parliament passed a bill (1714) "for provid- 
ing a publick reward for such person or persons as shall discover the 
Longitude." It was the largest reward ever offered, and stated that for 
any practical invention the following sum would be paid: 

£10,000 for any device that would determine the longitude within 1 
degree. 

£15,000 for any device that would determine the longitude within 40 
minutes. 

£20,000 for any device that would determine the longitude within 30 
minutes (2 minutes of time or 34 miles). 



234 



As though aware of the absurdity of their terms. Parliament authorized 
the formation of a permanent commission — the Board of Longitude — and 
empowered it to pay one half of any of the above rewards as soon as a 
majority of its members were satisfied that any proposed method was 
practicable and useful, and that it would give security to ships within 
eighty miles of danger, meaning land. The other half of any reward would 
be paid as soon as a ship using fte device should sail from Britain to a 
port in the West Indies without erring in her longitude more than the 
amounts specified. Moreover, the Board was authorized to grant a smaller 
reward for a less accurate method, provided it was practicable, and to 
spend a sum not to exceed £2000 on experiments which might lead to a 
useftil invention. 

For fifty years this handsome reward" stood untouched, a prize for the 
impossible, the Initt of English humorists and satirists. M^aiines and 
newspapers used it as a stock cliche. The Board of Longitude failed to see 
the joke. Day in and day out they were hounded by fools and charlatans, 
the perpetual motion lads and the geniuses who could quarter a circle and 
trisect an angle. To handle the flood of crackpots, they employed a secre- 
tary who handed out stereotyped replies to stereotyped proposals. The 
members of the Board met three times a year at the Admiralty, contribut- 
ing their services ami their time to the Crown, They took their responsibil- 
ities seriously and frequently called in consultants to help them appraise a 
promising invention. They were generous with grants-in-aid to struggling 
inventors with sound ideas, but what they demanded was results. Neither 
the Board nor any one else knew exactly what they were looking for, but 
what everyone knew was that the longitude problem had stopped the best 
minds in Europe, including Newton, Halley, Huygens, von Leibnitz and 
all the rest. It was solved, finally, by a ticking machine in a box, the inven- 
tion of an uneducated Yorkshire carpenter named John Harrison. The de- 
vice was the marine chronometer. 

Early clocks fell into two general classes: nonportable timekeepers 
driven by a falling weight, and portable timekeepers such as table clocks 
and crude watches, driven by a coiled spring. Gemma Frisius suggested 
the latter for use at sea, but with reservations. Knowing the unreliable 
temperam^t of spring-driven timekeepers, he admitted that sand and 
water clocks would have to be carried along to check the error of a spring- 
driven machine. In Spain, during the reign of Philip II, clocks were so- 
licited which would run exactly twenty-four hours a day, and many 
dififoent kinds had been invented. According to Alonso de Santa Cmz 
there were ''some with wheels, chains and weights of steel: some with 
chains of catgut and steel: others using sand, as in sandglasses: others 
with water in place of sand, and designed after many different fashions: 



m 

Edttlor's fioee: The prize wis equal to about 6 million 1994 dollars. 



John Harrison's "Ticking Box" 



others again with vases or large glasses filled with quicksilver: and, lastly, 
some, the most ingenious of all, driven by the force of die wind, which 
moves a weight and thereby the chain of the clock, or which are moved by 
the flame of a wick saturated with oil: and all of them adjusted to measure 
twenty-four hours exactly.'* 

Robert Hooke beoune interested in the development of poitable time- 
keepers for use at sea about the time Huygens perfected the pendulum 
clock. One of the most versatile scientists and inventors of all time, Hooke 
was one of those rare mechanical geniuses who was equally clever with a 
pen. After studying the faults of current timekeepers and the posfiiMky of 
building a more accurate one, he slyly wrote a summary of his investiga- 
tions, intimating that he was completely baffled and discouraged. "All I 
could obtain,'* he said, "was a Catalogs of Difficulties, first in the doing 
of it, secondly in the bringing of it into publick use, thirdly, in making 
advantage of it. Difficulties were proposed from the alteration of 
Climates, Airs, heats and colds, temperature of Springs, the nature of 
Vibrations, the wearing of Materials, the motion of tte Ship, and divers 
others." Even if a reliable timekeeper were possible, he concluded, **it 
would be difficult to bring it to use, for Sea-men know their way already 
to any Port. . . As for the rewards: "the Praemium for the Longitude," 
there never was any such thing, he retorted scornfully. "No King or State 
would pay a farthing for it.'* 

In spite of his pretended despondency, Hooke nevertheless lectured in 
1664 on the subject of applying springs to the balance of a wMch in onJer 
to render its vibrations more uniform, and demonstrated, with models, 
twenty different ways of doing it. At the same time he confessed that he 
had one or two other methods up his sleeve which he hoped to cash in on 
at some future date. Like many scientists of the time, Hooke expressed 
the principle of his balance spring in a Latin anagram; roughly: Ut tensio, 
sic vis, "as the tension is, so is the force," or, "the force exerted by a 
spring is directly proportional to the extent to which it is tensioned." 

The first timekeeper designed specifically for use at sea was made by 
Christian Huygens in 1660. The escapement was controlled by a pendu- 
lum instead of a spring balance, and like many of the clocks that followed, 
it proved useless except in a flat calm. Its rate was unpredictable; when 
tossed around by the sea it either ran in jerks or stopped altogether. The 
length of the pendulum varied with changes of temperature, and the rate 
of going changed in different latitudes, for some mysterious reason not yet 
determined. But by 1715 every physical principle and mechanical part that 
would have to be incorporated in an accurate timekeeper was understood 
by watchmakers. All that remained was to bridge the gap between a good 
clock and one that was nearly perfect. It was that half degree of longtaide, 
that two minutes of time, which meant the difference between conquest 
and failure, the difference between £20,000 and just another timekeeper. 

One of the biggest hurdles between watchmakers and the prize money 
was the weather: temperature and humidity. A few men included baro- 



236 



metric pressure. Without a doubt, changes in the weather did things to 
clocks and watches, and many suggestions were forthcoming as to how 
this principal source of trouble could be overcome. Stephen Plank and 
William Palmer, watchmakers, proposed keeping a timekeeper close to a 
fire, thus obviating errors due to change in temperature. Plank suggested 
keeping a watch in a brass box over a stove which would always be hot. 
He claimed to have a s^ret process for keeping Hie temperature of the 
fire uniform. Jeremy Thacker, inventor and watchmaker, published a 
book on the subject of the longitude, in which he made some caustic re- 
marks about the efforts of his contemporaries. He suggested that one of 
his colleagues, who wanted to test his clock at sea, should first arrange to 
have two consecutive Junes equally hot at every hour of every day. An- 
other colleague, referred to as Mr. Br ... e, was dubbed the Corrector of 
the Moon^s Motion. In a more serious vein, ITiacker made several sage 
observations regarding the physical laws with which watchmakers were 
struggling. He verified experimentally that a coiled spring loses strength 
when heated and gains it when cooled. He kept his own clock under a 
kind of bell jar connected with an exhaust pump, so that it could be run 
in a partial vacuum. He also devised an auxiliary spring which kept the 
clock going while the mainspring was being wound. Both springs were 
wouikI cmtside the bell by means of rods passed through stuffing boxes, 
so that neither the vacuum nor the clock mechanism would have to be 
disturbed. In spite of these and other devices, watchmakers remained in 
the dark and their problems remained unsolved until John Harrison went 
to work on the physical laws behind them. After that they did not seem so 
difficult. 

Harrison was bom at Foulby in the parish of Wragby, Yorkshire, in 
May, 1 693. He was the son of a carpenter and joiner in the service of Sir 
Rowland Winn of Nostell Priory. John was the oldest son in a large family. 
When he was six years old he contracted smallpox, and while convalesc- 
ing spent hours watching the mechanism and listening to the ticking of a 
watch laid on his pillow. When his family moved to Barrow in Lincoln- 
shire, John was seven years old. There he learned his father's trade and 
worked with him for several years. Occasionally he earned a little extra by 
surveying and measuring land, but he was much more interested in me- 
chanics, and spent his evenings stodying Nicholas Saunderson's published 
lectures on mathematics and physics. These he copied out in longhand 
including all the diagrams. He also studied the mechanism of clocks and 
watches, how to repair them and how they miglrt be improved. In 1715, 
when he was twenty-two, he built his first grandfather clock or "regula- 
tor" The only remarkable feature of the machine was that all the wheels 
except the escape wheel were made of oak, with the teeth, carved sepa- 
rately, set into a groove in the rim. 

Many of the mechanical faults in the clocks and watches that Harrison 
saw around hirn were caused by the expansion and contraction of the 
metals used in their construction. Pendulums, for example, were usually 



Joha Harrison's 'Ticking Box" 



made of an iron or steel rod with a lead bob fastened at the end. In winter 
the rod contracted and the clock went fast, and in summer the rod 
expanded, making the clock lose time. Harrison made his first mqxMtant 
contribution to clockmaking by developing the "gridiron" pendulum^ so 
named because of its appearance. Brass and steel, he knew, expand for a 
given increase in temperature in Ae ratio of about three to two ( 100 to 
62). He therefore built a pendulum with nine alternating steel and brass 
rods, so pinned together that expansion or contraction caused by variation 
in the temperature was eliminated, the unlike rods counteracting each 
other. 

The accuracy of a clock is no greater than the efficiency of its escape- 
ment, the piece which releases for a second, more or less, the driving 
power, such as a suspended weight or a coiled mainspring. One day 
Harrison was called out to repair a steeple clock that refused to run. After 
looking it over he discovered that all it needed was some oil on the pal- 
lets of the escapement. He oiled the mechanism and soon after went to 
work on a design for an escapement that would not need oiling. The re - 
sult was an ingenious "grasshopper" escapement that was very nearly 
frictionless and also noiseless. However, it was extremely delicate, un- 
necessarily so, and was easily upset by dust or unnecessary oil. These 
two improved parts alone were almost enough to revolutionize the cloek- 
making industry. One of the first two grandfather clocks he built that 
were equipped with his improved pendulum and grasshopper escapement 
did not gain or lose more than a second a month during a period of four- 
teen years. 

Harrison was twenty-one years old when Parliament posted the £20,000 
reward for a reliable method of determining longitude at sea. He had not 
finished his first clock, and it is doubtful whether he seriously asfrired to 
winning such a fortune, but certainly no young inventor ever had such a 
fabulous goal to shoot at, or such limited competition. Yet Harrison never 
hurried his work, even after it must have been apparent to him that the 
prize was almost within his reach. On the contrary, his real god was the 
perfection of his marine timekeeper as a precision instrument and a thing 
of beauty. The monetary reward, therefore, was a foregone conclusion. 

His first two fine grandfather clocks were completed by 1726, when he 
was thirty-three years old, and in 1 728 he went to London, carrying with 
him full-scale models of his gridiron pendulum and grasshopper escape- 
ment, and working drawings of a marine clock he hoped to build if he 
could get some financial assistance from the Board of Longitude. He 
called on Edmund Halley, Astronomer Royal, who was also a member of 
the Board. Halley advised him not to depend on the Board of Longitude, 
but to talk things over with George Graham, England's leading horolo- 
gist. Harrison called on Graham at ten o'clock one morning, md together 
they talked pendulums, escapements, remontoires and springs until eight 
o'clock in the evening, when Harrison departed a happy man. Graham 
had advised him to build his clock first and then apply to the Board of 



238 



Longitude. He had also offered to loan Harrison the money to build it 
with, and would not listen to any talk about interest or security of any 
kindi Hiaumon went home to Barrow md spent the n^t seven years 
building his first marine timekeeper; his ''Number One," as it was later 

called. 

In addition to heat and cold, the archenemies of all watchmakers, he 
concttfitrated on elitninating friction, or cutting it down to a bare mini- 
mum, on every moving part, and devised many ingenious ways of doing 
it; some of them radical departures from accepted watchmaking practice. 
Instead of using a pendulum, which would be impractical at sea, Harrison 
designed two huge balances weighing about five pounds each, that were 
connected by wires running over brass arcs so that their motions were 
always opposed. Thus any effect on one produced by the motion of the 
ship would be counteracted by the other. The "grasshopper" escapement 
was modified and simplified and two mainsprings on separate drums were 
installed. The clock was finished in 1735. 

There was nothing beautiful or graceful about Harrison's Number One. 
It weighed seventy-two pounds and looked like nothing but an awkward, 
unwieldy piece of machinery. However, everyone who saw it and studied 
its mechanism declared it a masterpiece of ingenuity, and its performance 
certainly belied its appearance. Harrison mounted its case in gimbals and 
for a while tested it unofficially on a barge in the Humber River. Then he 
took it to London where he enjoyed his first brief triumph. Five members 
of the Royal Society examined the clock, studied its mechanism and then 
presented Harrison with a cenificate stating that the principles of this 
timekeeper promised a sufficient degree of accuracy to meet the require- 
ments set forth in the Act of Queen Anne. This historic document, which 
opened for Harrison the door to the Board of Longitude, was signed by 
HaHey, Smith, Bradley, Machin and Graham. 

On the strength of the certificate, Harrison applied to the Board of 
Longitude for a trial at sea, and in 1736 he was sent to Lisbon in H.M.S. 
Centurion, Captain Proctor. In his possession was a note from Sir Charles 
Wager, First Lord of the Admiralty, asking Proctor to see that every cour- 
tesy be given the bearer, who was said by those who knew him best to be 
'*a very ingenious and sober man.'" Harrison was given the run of the ship, 
and his timekeeper was placed in the Captain's cabin where he could 
make observations and wind his clock without interruption. Proctor was 
courteous but skeptical. "The difficulty of measuring Time truly," he 
wrote, "where so m^y unequal Shocks and Motions stmd in Opposition 
to it, gives me concern for the honest Man, and makes me feel he has 
attempted Impossibilities." 

No record of the clock's going on the outward voyage is known, Imt 
after the return trip, made in H.M.S. Oxford, Robert Man, Harrison was 
given a certificate signed by the master (that is, navigator) stating: "When 
we made the land, the said land, according to my reckoning (and others), 
ought to have been the Start; but before we knew what land it was, John 



J<*n Harrison's "Ticking Box" 



Harrison declared to me and the rest of the ship's company, that accord- 
ing to his observations with his machine, it ought to be the Lizard — ^the 
which, indeed, it was found to be, his observation showing the sh^ to be 
more west than my reckoning, above one degree and twenty-six miles." It 
was an impressive report in spite of its simplicity, and yet the voyage to 
Lisbon and return was made in practically a north and south direction; 
one that would hardly demonstrate the best qualities of the clock in the 
most dramatic fashion. It should be noted, however, that even on this 
well-worn trade route it was not considered a scandal that the ship's navi- 
gator should make an enror of 90 miles in his landfdl. 

On June 20, 1737, Harrison made his first bow to the mighty Board of 
Longitude, According to the official minutes, "Mr. John Harrison pro- 
duced a new invented machine, in the nature of clockwork, whereby he 
proposes to keep time at sea with more exactness than by any other in- 
strument or method hitherto contrived . . . and proposes to make another 
machine of smaller dimensions within the space of two years, whereby 
he will endeavour to correct some defects which he hath found in that 
already prepared, so as to render the same more perfect . . The Board 
voted him £500 to help defray expenses, one half to be paid at once and 
the other half when he completed the second clock and delivered same 
into the hands of one of His Majesty's ship's captains. 

Harrison's Number Two contained several minor mechanical improve- 
ments and this time all the wheels were made of brass instead of wood. In 
some respects it was even more cumbersome than Number One, and it 
weighed one hundred and three pounds. Its case and gimbal suspension 
weighed another sixty-two pounds. Number Two was finished in 1739, 
but instead of turning it over to a sea captain appointed by the Board to 
receive it, Harrison tested it for nearly two years under conditi<ms of 
**great heat and motion," Number Two was never sent to sea because by 
the time it was ready, England was at war with Spain and the Admiralty 
had no desire to give the Spaniards an opportunity to capture it. 

In January, 1741 , Harrison wrote the Board that he had begun work on 
a third clock which promised to be far superior to the first two. They 
voted him another £500. Harrison struggled with it for several months, 
but seems to have miscalculated the "moment of inertia" of its balances. 
He thought he could get it going by the first of August, 1741, and have it 
ready for a sea trial two years later. But after five years the Board learned 
*'that it does not go well, at present, as he expected it would, yet he 
plainly perceived the Cause of its present Imperfection to lye in a certain 
part [the balances] which, being of a different form from the correspond- 
ing part in the other machines, had never been tried before." Harrison had 
made a few improvements in the parts of Number Three and had incorpo- 
rated in it the same antifriction devices he had used on Number Two, but 
the clock was still bulky and its parts were far from delicate; the machine 
weighed sixty-six pounds and its case and gimbals another thirty-five. 



240 



Harrison was again feeling the pinch, even though the Board had given 
him several advances to keep him going, for in 1746, when he reported on 
Number Three, he laid before the Board an impressive testimonial signed 
by twelve members of the Royal Society including the President, Martin 
Folkes, Bradley, Graham, Halley and Cavendish, attesting the importance 
and practical value of his inventions in the solution of the longitude prob- 
lem. Presumably this gesture was made to insure the financial support of 
the Board of Longitude. However, the Board needed no prodding. Three 
years later, acting on its own volition, the Royal Society awarded Harrison 
the Copley meded, the highest honor it could bestow. His modesty, perse- 
verance and skill made them forget, at least for a time, the total lack of 
academic background which was so highly revered by that august body. 

Convinced that Number Three would never satisfy him, Harrison pro- 
posed to start work on two more timekeepers, even before Number Three 
was given a trial at sea. One would be pocketsize and the other slightly 
larger. The Board approved the project ^d Harrison went ahead. Aban- 
dojEUAg the idea of a pocketsize chronometer, Harrison decided to concen- 
trate his efforts on a slightly larger clock, which could be adapted to the 
intricate mechanism he had designed without sacrificing accuracy. In 
1757 he began work on Number Four, a machine which "by reason alike 
of its beauty, its accuracy, and its historical interest, must take pride of 
place as the most famous chronometer that ever has been or ever will be 
made." It was finished in 1759. 

Number Four resembled an enormous "pair-case" watch about five 
inches in diameter, complete with pendant, as though it were to be worn. 
The dial was white enamel with an ornamental design in black. The hour 
and minute hands were of blued steel and the second hand was polished. 
Iit^iead of a gimbal suspension, which Harrison had come to distrust, he 
used only a soft cushion in a plain box to support the clock. An adjustable 
outer box was fitted with a divided arc so that the timekeeper could be 
kept in the same position (with the pendant always slightly above the 
horizontal) regardless of the lie of the ship. When it was finished, Number 
Four was not adjusted for more than this one position, and on its first 
voyage it had to be carefully tended. The watch beat five to the second 
and ran for thirty hours without rewinding. The pivot holes were jeweled 
to the third wheel with rubies and the end stones were diamonds. En- 
graved in the top-plate were the words "John Harrison & Son, A.D. 
1759." Cunningly concealed from prying eyes beneath the plate was a 
mechanism such as the world hai never seen; every pinion and bearing, 
each spring and wheel was the end product of careful planning, precise 
measurement and exquisite craftsmanship. Into the mechanism had gone 
"fifty years of self-denial, unremitting toil, and ceaseless concentration,'* 
To Harrison, whose singleness of purpose had made it possible for him to 
achieve the impossible. Number Four was a satisfactory climax to a life- 
time of effort. He was proud of this timekeeper, and in a rare burst of 



John Harrison's "Ticking Box" 



eloquence he wrote, "I think I may make bold to say, that there is neither 
any other Mechanical or Mathematical thing in the World that is more 
beautiful or curious in texture than this my watch or Time-fc^^r for the 
Longitude . . . and I heartily thank Almighty God that I have lived so 
long, as in some measure to complete it." 

After checking and adjusting Number Four with his pendulum clock 
for nearly two years, Harrison reported to the Board of Longitude, in 
March 1761 , that Number Four was as good as Number Three and that its 
performance greatly exceeded his expectations. He asked for a trial at sea. 
His request was granted, and in April, 1761, William Harrison, hh son 
and right-hand man, took Number Three to Portsmouth. The father ar- 
rived a short time later with Number Four. There were numerous delays 
at Portsmouth, and it was October before passage was finally arranged for 
young Harrison aboard H.M.S. E>eptford, Dudley Digges, bound for 
Jamaica. John Harrison, who was then sixty-eight years old, decided not 
to attempt the long sea voyage himself; and he also decided to stake 
everything on the performance of Number Four, instead of sending both 
Three and Four along. The Deptford finally sailed from Spithead with 
a convoy, November 18, 1761, after first touching at Portland and Ply- 
mouth. The sea trial was on. 

Number Four had been placed in a case with four locks, and the four 
keys were given to William Harrison, Governor Lyttleton of Jamaica, who 
was taking passage on the Deptford, Captain Digges, and his first lieu- 
tenant. AH four had to be present in order to open the case, even for wind- 
ing. The Board of Longitude had further arranged to have the longitude of 
Jamaica determined de novo before the trial, by a series of obser\ ations 
of the satellites of Jupiter, but because of the lateness of the season it was 
decided to accept the best previously established reckoning. Local time at 
Portsmouth and at Jamaica was to be determined by taking equal alti- 
tudes of the sun, and the difference compared with the time indicated by 
Harrison ' s timekeeper. 

As usual, the first scheduled port of call on the run to Jammca was 
Madeira. On this particular voyage, all hands aboard the Deptford were 
anxious to make the island on the first approach. To William Harrison it 
meant the first crucial test of Number Four; to Captain Digges it meant a 
test of his dead reckoning against a mechanical device in which he had no 
confidence; but the ship's comply had more than a scientific interest in 
the proceedings. They were afraid of missing Madeira altogether, "the 
conseqtience of which, would have been Inconvenient," To the horror of 
all hands, it was found that the beer had spoiled, over a thousand gallons 
of it, and the people had already been reduced to drinking water. Nine 
days out from Plymouth the ship's longitude, by dead reckoning, was 
13° 50' west of Greenwich, but according to Number Four and William 
Harrison it was 15° 19' W. Captain Digges naturally favored his dead 
reckoning ealculations, but Harrison stoutly maintained that Number Four 
was right and that if Madeira were properly marked on the chart thQr 



242 



would sight it the next day. Although Digges offered to bet Harrison five 
to one that he was wrong, he held his course, and the following morning 
at 6 A.M. the lookout sighted Porto Santo, the northeastern island of the 
Madeira group, dead ahead. 

The Deptford's officers were greatly impressed by Harrison's uncanny 
predictions throughout the voyage. They were even more impressed when 
they arrived Jamaica three days before H.M,S. Beaver, which had 
sailed for Jamaica ten days before them. Number Four was promptly 
taken ashore and checked. After allowing for its rate of going (2M seconds 
per day losing at Portsmouth), it was found to be 5 seconds slow, an error 
in longitude of 1%' only, or 1J4 nautical miles. 

The official trial ended at Jamaica. Arrangements were made for 
William Hamson to make the return voyage in the Merlin, sloop, and in a 
burst of enth^iasm Caplam Digges placed his order for the first Harrison- 
built chronometer which should be offered for sale. The passage back to 
England was a severe test for Number Four. The weather was extremely 
rough and the timekeeper, still carefully tended by Harrison, had to be 
moved to the poop, the only dry place on the ship, where it was pounded 
unmercifully and "received a number of violent shocks." However, when 
it was again checked at Portsmouth, its total error for the five months' 
voyage* through heat and cold, fair weather and foul (after allowing for 
its rate of going), was only 1"" 53K°, or an error in longitude of 28M' (28!^ 
nautical miles). This was safely within the limit of half a degree specified 
in the Act of Queen Anne. John Harrison and son had won the fabulous 
reward of £20,000. 

The sea trial had ended, but the trials of John Harrison had just begun. 
Now for the first time, at the age of sixty-nine, Harrison began to feel the 
lack of an academic background. He was a simple man; he did not know 
the language of diplomacy, the gentle art of innuendo and evasion. He 
had mastered the longitude but he did not know how to cope with the 
Royal Society or the Board of Longitude. He had won the reward and 
all he wanted now was his money. The money was not immediately 
forthcoming. 

Neither the Board of Longitude nor the scientists who served it as 
consultants were at any time guilty of dishonesty in their dealings with 
Harrises; they were only human* £20,000 was a tremendous fortune, and 
it was one thing to dole out living expenses to a watchmaker in amounts 
not exceeding £500 so that he might contribute something or other to the 
general cause. But it was another thing to hand over £20,000 in a lump 
sum to one man, and a man of humble birth at that. It was most extraordi- 
nary. Moreover, there were men on the Board and members of the Royal 
Society who had designs on the reward themselves or at least a cut of it. 
James Bradley and Johann Tobias Mayer had both worked long and hard 
on the compilation of accurate lunar tables. Mayer's widow was paid 
£3000 for his contribution to the cause of longitude, and in 1761 Bradley 
told Harrison that he and Mayer would have shared £10,000 of the prize 



J<*n Harrison's "ricking Box" 



money between them if it had not been for his blasted watch. Halley had 
straggled long and manfully on the solution of the longitude by compass 
variation, and was not in a position to ignore any part of £20^060. The 
Reverend Nevil Maskelyne, Astronomer Royal, and compiler of the Nau- 
tical Almanac, was an obstinate and uncompromising apostle of "lunar 
distances" or "lunars" for finding the longitude, and had closed Ms mind 
to any other method whatsoever. He loved neither Harrison nor his 
watch. In view of these and other unnamed aspirants, it was inevitable 
that the Board should decide that the amazing performance of Harrison's 
timekeeper was a fluke. They had never been allowed to examine the 
mechanism, and they pointed out that if a gross of watches were carried 
to Jamaica under the same conditions, one out of the lot might perform 
equally well — ^at least for one trip. They accordingly refused to give 
Harrison a certificate stating that he had met the requirements of the Act 
until his timekeeper was given a further trial, or trials. Meanwhile, they 
did agree to give him the sum of £2500 as an interim reward, since his 
machine had proved to be a rather useful contraption, though mysterious 
beyond words. An Act of Parliament (Febmary, 1 763) enabling him to 
receive £5000 as soon as he disclosed the secret of his invention, was 
completely nullified by the absurdly rigid conditions set up by the Board, 
He was finally granted a new trial at sea. 

The rales laid down for the new trial were elaborate and exacting. The 
difference in longitude between Portsmouth and Jamaica was to be deter- 
mined de novo by observations of Jupiter's satellites. Number Four was to 
be rated at Greenwich before sailing, but Harrison balked, saying "that 
he did not chuse to part with it out of his hands till he shall have reaped 
some advantage from it." However, he agreed to send his own rating, 
sealed, to the Secretary of the Admiralty before the trial began. After end- 
less delays the trial was arranged to take place between Portsmouth and 
Barbados, instead of Jamaica, and William Harrison embarked on Febra- 
ary 14, 1764, in H.M.S. Tartar, Sir John Lindsay, at the Nore. TTie Tartar 
proceeded to Portsmouth, where Harrison checked the rate of Number 
Four with a regulator installed there in a temporary observatory. On 
March 28, 1764, the Tartar sailed from Portsmouth and the second trial 
was on. 

It was the same story all over again. On April 18, twenty-one days out, 
Harrison took two altitudes of the sun and announced to Sir John that 
they were forty-three miles east of Porto Santo. Sir John accordingly 
steered a direct course for it, and at one o'clock the next morning the 
island was sighted, "which exacdy agreed with the Distance mentioned 
above." They arrived at Barbados May 13, "Mr, Harrison all along in the 
Voyage declaring how far he was distant from that Island, accordmg to 
the best settled longitude thereof. The Day before they made it, he de- 
clared the Distance: and Sir John sailed in Consequence of this Declar- 
ation, till Eleven at Night, w^bich proving dark he thought proper to lay 
by. Mr. Harrison ±en declaring they were no more than eight or nine 



244 



Miles from the Land, which accordingly at Day Break they saw from that 

Dis^ce" 

When Harrison went ashore with Number Four he discovered that 
none other than Maskelyne and an assistant. Green, had been sent ahead 
to check the longitude of Barbados by observing Jupiter's satellites. 
Moreover, Maskelyne had been orating loudly on the superiority of his 
own method of fiiniing longitude, namely by lunar distances. When 
Harrison heard what had been going on he objected strenuously, pointing 
out to Sir John that Maskelyne was not only an interested party but an 
active and avid competitor, and should not have anything to do with the 
trials. A compromise was arranged, but, as it turned out, Maskelyne was 
suddenly indisposed and unable to make the observations. 

After comparing the data obtained by observation with Harrison's 
chronometer, Number Four showed m error of 38.4 seconds over a period 
of seven weeks, or 9.6 miles of longitude (at the equator) between Ports- 
mouth and Barbados. And when the clock was again checked at Ports- 
mouth, after 156 days, elapsed time, it showed, after allowing for its rate 
of going, a total gmn of only 54 seconds of time. If furfter allowance 
were made for changes of rate caused by variations in temperature, infor- 
mation posted beforehand by Harrison, the rate of Number Four would 
have been reduced to an error of 15 seconds of loss in 5 months, or less 
than Vio of a second a day. 

The evidence in favor of Harrison's chronometer was overwhelming, 
and could no longer be ignored or set aside. But the Board of Longitude 
was not through. In a Resolution of Febmary 9, 1765, they were unani- 
mously of the opinion that **the said timekeeper has kept its time with 
sufficient correctness, without losing its longitude in the voyage from 
Portsmouth to Barbados beyond the nearest limit required by the Act 12th 
of Queen Anne, but even considerably within the same." Now, they said, 
all Harrison had to do was demonstrate the mechanism of his clock and 
explain the construction of it, '*by Means whereof other such Time- 
k^ers might be framed, of sufficient Correctness to find the Longitude 
at Sea. , , In order to get the first £10,000 Harrison had to submit, on 
oath, complete working drawings of Number Four; explain and demon- 
strate the operation of each part, including the process of tempering the 
springs; and finally, hand over to the Board his first three timekeepers as 
well as Number Four. 

Any foreigner would have acknowledged defeat at this juncture, but not 
Harrison, who was an Englishman and a Yorkshireman to boot. "I cannot 
help thinking," he wrote the Board, after hearing their harsh terms, *'but I 
am extremely ill used by gentlemen who I might have expected different 

treatment from It must be owned that my case is very hard, but I hope 

I am the first, and for my country's sake, shall be the last that suffers by 
pinning my faith on an English Act of Parliament." The case of **Lon- 
gitude Harrison" began to be aired publicly, and several of his friends 
launched an impromptu publicity campaign against the Board and against 



John Harrison's "Ticking Box" 



Parliament. The Board finally softened their terms and Harrison reluc- 
tantly took his clock apart at his home for the edification of a committee 
of six» nominated by the Board; tiiree of them, Tliomas Mudge, William 
Matthews and Larcum Kendall, were watchmakers. Harrison then re- 
ceived a certificate from the Board (October 28, 1765) entitling him to 
£7500, or the balance due him on the first half of the reward. The second 
half did not come so easily. 

Number Four was now in the hands of the Board of Longitude, held in 
trust for the benefit of the people of England. As such, it was carefully 
guarded against prying eyes and tampering, even by members of the 
Board. However, that learned body did its humble best. First they set out 
to pubUcize its mechanism as widely as possible. Unable to take the thing 
apart themselves, they had to depend on Harrison's own drawings, and 
these were redrawn and carefully engraved. What was supposed to be a 
full textual description was written by the Reverend Nevil Maskelyne and 
printed in book form with illustrations appended: The Principles of Mr. 
Harrison's Time«Keeper, with Plates of the Same. London, 1767. Actually 
the book was harmless enough, because no human being could have even 
begun to reproduce the clock from Maskelyne's description. To Harrison 
it was just another bitter pill to swallow. "They have since published all 
my Drawings," he wrote, "wittiout giving me the last Moiety of fte Re- 
ward, or even paying me and my Son for Our Time at a rate as common 
Mechanicks; an Instance of such Cruelty and Injustice as I believe never 
existed in a learned and civilised Nation before." Other galling experi- 
ences followed. 

With great pomp and ceremony Number Four was carried to the Royal 
Observatory at Greenwich. There it was scheduled to undergo a prolonged 
and exhaustive series of trials under the direction of the Astronomer 
Royal, the Reverend Nevil Maskelyne. It cannot be said that Maskclyne 
shirked his duty, although he was handicapped by the fact that the time- 
keeper was always kept locked in its case, and he could not even wind il 
except in the presence of an officer detailed by the Governor of Green- 
wich to witness the performance. Number Four, after all, was a £10,000 
timekeeper. The tests went on for two months. Maskelyne tried the watch 
in various positions for which it was not adjusted, dial up md didi down. 
Then for ten months it was tested in a horizontal position, dial up. The 
Board published a full account of the results with a preface written by 
Maskelyne, in which he gave it as his studied opinion "That Mr. Harri- 
son's Watch cannot be depended upon to keep the Longitude within a 
Degree, in a West-India Voyage of six weeks, nor to keep the Longitude 
within a Half a Degree for more than a Fortnight, and then it must be kept 
in a Place where the Thermometer is always some Degrees above freez- 
ing." (There was still £10,000 prize money outstanding.) 

The Board of Longitude next conunissioned Larcum Kendall, watch- 
maker, to make a duplicate of Number Four. They also advised Harrison 
that he must make Number Five and Number Six and have them tried at 



2m 



sea, intimating that otherwise he would not be entitled to the other half of 
the reward. When Harrison asked if he might use Number Four for a short 
time to help him build two copies of it, he was told that Kendall needed 
it to work from and that it would be impossible. Harrison did the best 
he could, while the Board laid plans for an exhaustive series of tests for 
Nittnber Five and Number Six. They spoke of sending them to Hudson's 
Bay and of letting fliem toss and pitch in the Downs for a month or two as 
\s c\l as sending them out to the West Indies. 

After three years (1767-1770) Number Five was finished. In 1771, just 
as the HarrisiCWls were finishing the last adjustments on the clock, they 
heard that Captain Cook was preparing for a second exploring cruise, and 
that the Board was planning to send Kendall's duplicate of Number Four 
along with him. Harrison pleaded with them to send Number Four and 
Number Five instead, telling them he was wiUing to stake his claim to the 
balance of the reward on their performance, or to submit "to any mode of 
trial, by men not already proved partial, which shall be definite in its na- 
ture." The man was now more than ever anxious to settle the business 
oilce and for all. But it was not so to be. He was told that the Board did 
not see fit to send Number Four out of the kingdom, nor did they see any 
reason for departing from the manner of trial already decided upon. 

John Harrison was now seventy-eight years old. His eyes were failing 
and his skilled hands were not as steady as they were, but his heart was 
strong and there was still a lot of fight left in him. Among his powerful 
friends and admirers was His Majesty King George the Third, who had 
granted Harrison and his son an audience after the historic voyage of 
the Tartar. Harrison now sought the protection of his king, and "Farmer 
George," after hearing the case from start to finish, lost his patience. "By 
God, Harrison, I'll see you righted," he roared. And he did. Number Five 
was tried at His Majesty's private observatory at Kew. The king attended 
the daily checking of the clock's performance, and had the pleasure of 
watching the operation of a timekeeper whose total error over a ten 
week's period was 4M seconds. 

Harrison submitted a memorial to the Board of Longitude, November 
28, 1772, describing in detail the circumstances and results of the trial at 
Kew. In return, the Board passed a resolution to the effect that they were 
not the slightest bit interested; that they saw no reason to alter the manner 
of trial they had already proposed and that no regard would be paid for a 
trial made under any other conditions. In desperation Harrison decided to 
play his last card — ^the king. Backed by His Majesty's personal interest in 
the proceedings, Harrison presented a petition to the House of Commons 
with weight behind it. It was heralded as follows: "The Lord North, by 
His Majesty's Command, acquainted the House that His Majesty, having 
been informed of the Contents of the said Petition, recommended it to the 
Consideration of the House." Fox was present to give the petition his fiill 
support, and the king was willing, if necessary, to appear at the Bar of the 
House under an inferior title and testify in Harrison's behalf. At the same 



John Harrison's "Ticking Box" 



time, Harrison circulated a broadside. The Case of Mr. John Harrison, 
stating his claims to the second half of the reward. 

The Board of Longitude began to squirm. Public indignation was 
mounting rapidly and the Speaker of the House informed the Board that 
consideration of the petition would be deferred until they had an opportu- 
nity to revise their proceedings in regard to Mr. Harrison, Seven Admiralty 
clerks were put to work copying out all of the Board's resolutions con- 
cerning Harrison. While they worked day and night to finish the job, the 
Board made one last desperate effort. They summoned William Harrison 
to appear before them; but the hour was late. They put him through a cate- 
chism and tried to make him consent to new trials and new conditions. 
Harrison stood fast, refusing to consent to anything they might propose. 
Meanwhile a money bill was drawn up by Parliament in record time; the 
king gave it the nod and it was passed. The Harrisons had won tiheir fight. 



248 



Part Four 



Guidance and Commentary 



The book concludes with six chapters offering guidance and commentary, 
Eric Swanson, long a proponent of "Moore's Law," explains why he feels 
this law dominates all design approaches. John Willison advises on all 
sorts of things in a highly efficient and far-ranging editorial. Jim Williams 
explains why a laboratory in your home can be an invaluable intellectual 
and economic investment, and provides details on how to assemble a lab. 

In an especially memorable essay, Barrie Gilbert discusses how to 
promote innovation in the IC business. The chapter is an elegant answer 
to a world full of managerial "methods" which purport to systematize 
innovation. 

Carl Nelson discusses combining loose thinking with strict confor- 
mance to mother nature's laws to produce good circuits. Art Delagrange 
expresses similar views, with examples drawn from a lifetime of design 
work. 



249 



This page intentionally left blank 



Eric Swanson 



15. Moore's Law 



Call me a heretic, but in the late 1970s, long before I'd heard of Philbrick, 
Widl£ff, or GSIbert, I learned about Moore's Law, Gordon Moore came 
down to a VLSI conference at Caltech armed with a "moon curve" some- 
what like that shown in Figure 15-L His message was simple: memory 
density increases fourfold every three years. Run the linear-year versus 
log-density curve out for a couple of deczdes, and you reach levels of 
integration so fabulous that you might as well be at the moon. 

Moore also claimed that increases in memory density trickle down to 
less significant areas like microprocessors, and he challenged the design 
community to try to ISgure out what on earth to do with all those extra 
transistors. Fifteen years later, the minicomputer is dead, Moore's Intel is 
very big, and, just like clockwork, memories are a thousand times denser. 
The analog-oriented readers of this book may appreciate the following 
memory aids. Chip complexity increases 4X every three years, 12dB 
every three years, 4dB/year, 40dB/decade. Integration, it seems, is a 
second-order high-pass filter. 



10 



,10 




Figure 15-1. 
A moon curve. 



1980 



1985 



1990 



1995 



2000 



year 



251 



For me, learning Moore's Law before moving on to analog circuits 
proved very helpful. Moore's Law gives digital designers a drive to obso- 
lete the past, and to do so quickly. A 64K DRAM designer knew better 
than to rest on his laurels, lest Moore's Law run him over. Young digital 
designers know that their first chips must whip the old guys' chips. In 
contrast, the analog design community takes the view that its new kids 
may approach, with time, the greatness of the old guys. That view is 
wrong; our expectations for young designers should be set much higher. 

Fortunately, a good-sized piece of the analog IC business now follows 
Moore's Law. State-of-the-art mixed-signal circuits crossed the VLSI 
threshold of 10000 transistors around 1985. A decade later we're at the 
million-transistor level. Has the analog design business fundamentally 
changed? Are we reduced to button-pushing automatons? Is elegance 
gone? 

The next three sections attempt to answer such questions. First, we 
take a look at some of the competition between brute-force integration 
and design elegance. Elegance lives on, but brute force must be respected ! 
Next, we look at a few of the interesting subcircuits of analog CMOS. 
True to the analog tradition, state-of-the-art subcircuits are bom in the 
brain or in the lab, not on the workstation, never synthesized. Finally, 
we'll look at elegance at a different level, how analog circuits with thou- 
sands of transistors can have legitimate elegance of their own. 

Brute Fonse VS. Elegance 

The evolution of analog- to-digital converters bears an interesting re- 
lationship to MGore*s Law. Figure 15-2 plots the dynamic range of 
state-of-the-art analog-to-digital converters as a function of their sam- 
pling frequency. Over many decades of ADC speed, the world's best 
converter performance falls on a reasonably well-defixied line. The line 
doesn't stand still over the years; it moves upward. The rate of improve- 
ment has remained remarkably constant since the first monolithic convert- 
ers appeared in the mid 1970s. Transistors get faster and more numerous. 
CMOS technology rises to compete with bipolar. Power supply and signal 
voltages decrease. New architectures emerge and are perfected. And con- 
verter performance improves by a very predictable 2dB/year. 

Analog-to-digital converters are noisy by analog signal processing 
standards. Today's world-class converters have input-referred noise spec- 
tral densities of lOOnV/VSz or so. Perhaps ADC evolution will stop 
when converters reach the noise performance of, say, 50O resistors, but 
we won't reach such quasi-fundamental limits for a generation! Also, no 
matter how noisy analog-to-digital converters may be, they represent the 
only path from the analog world to decent-quality memory. 

What's the tie-in to Moore's Law? The Law gives us a 4X increase in 
ADC complexity every three years. We can take it easy for the next three 
years and simply integrate four of today's converters on a common sub- 



Eric Swanson 




strata. We*ll ecmnect the same analog signal to all four converter inputs 
and design some simple logic to add the four digital outputs every sam- 
pling period. If each converter's noise is dominated by thermal noise (un^ 
correlated from converter to converter), we get a 6dB improyement in 
dynamic range. The Moore's Law increase in integration underpins ADC 
improvement of 2dB/year! 

To my knowledge, brute-force replication of ADCs has never yielded 
a converter of worid-class performance. World-class converters exploit 
design cleverness to achieve lower manufacturing costs than brute-force 
alternatives. Yet the brute-force option serves as a competitive reminder 
to clever engineers— they had better not take too long to perfect their 
cleverness! 



Born m the Lab 

Certainly, the complexity of analog VLSI demands computer circuit sim- 
ulation. Circuit simulation hasn*t changed much over the years. Perhaps 
the only significant progress in this area comes from better computers. 
Solving big, nonlinear differential equations is still, after all, solving big, 
nonlinear dififerential equations. CAD tool vendors, ever-notorious for 
overhyping their products, claim that improved graphics interfaces trans- 
late into huge productivity increases, but in practice these interfaces add 
little. Now-obsolete batch-mode tools forced designers to think before 
sinmlation, and thinking is a very healthy thing. Today's 17-inch work- 
station monitors cannot display enough detail, nowhere near as much as 
yesterday's quarter-inch-thick printouts, and engineers must constantly 



253 



page from screen to screen. Graphics interfaces may be sexy and fun, but 
real progress comes from MIPS. 

Young engineers sometimes fall into the trap of thinking ttet compiiter 
simulations define reality. They cannot finalize a design before the simu- 
lations work. Unfortunately for them, certain problems that real circuits 
handle easily are very difficult for simulators. Charge conserva^on, criti- 
cal to analog CMOS design, is one such problem. When your simulator 
loses charge in a way that the real circuit cannot, it's time to discount the 
error and move on. The integrated circuit business is paid to ship real 
chips, not to have simulations match reality. The most vduabte design 
experience related to simulation is to be comfortable with its limitations! 

The best analog VLSI subcireuits are bom in the lab. Two of my fa- 
vorites appear below. The first involves a phenomenon not even modeled 
in SPICE, and the second looks at linearity levels so extreme that simula- 
tion will probably never be relevant. 

Comparator Memory 

Fve always been amused that the most accurate low-speed analog-to- 
digital converters are built from solid-state electronics' most nusmble 
low-frequency devices. Actually, that overstates the case. GaAs MESFETs 
are even worse than silicon MOSFETs, but CMOS devices are pretty bad. 
Start with poor device matching, maybe lOX worse than bipolar. Add in 
huge doses of 1/f noise. Complete the recipe with the power supply, tem- 
perature, and impedance sensitivities of charge injection. Small wonder 
the old bipolar companies thought they needed biCMOS to do anything 
useful! They were wrong; few state-of-the-art converters ever use 
biCMOS. Moore's Law is enough. 

Dave Welland's self-calibrated CS5016 contains wonderful architec- 
ture. The 5016 is a 16-bit, 5(MeHz, successive-approximation converter 
whose architecture dates back to 1984, building on early self-calibration 
work done by Dave Hodges and Hae-Seung Lee at Berkeley. All of these 
folks recognized the fact that, given enough transistors, an analog-to- 
digital converter could figure out all by itself how to divide up a refer- 
ence voltage into precisely equal pieces. The principle may be obvious, 
but the death is in the details. Noise constantly creeps in to corrupt the 
measurement of all those little pieces, and the effects of noise must be 
removed just right. 

Once the DAC inside the ADC is properly calibrated, the comparator 
is all that's left. Everyone knows that 1/f noise in the comparator is bad 
news. While CMOS l/f noise is bad, it's always eliminated by dtther 
autozeroing or chopping, and by now it's axiomatic in the design business 
that one of those two techniques can be counted on for any analog VLSI 
application. The 5016 autozeroes its comparator in a way we'll describe 
later. 



Eric Swanson 



A less-appreciated requirement for the comparator inside an S AR 
ADC is that it had better be memory less. For some analog inputs, the 
successive-approximation algorithm requires the comparator to make its 
most sensitive decision in the approximation cycle immediately following 
huge comparator overdrive. If the comparator has any memory at all, 
missing codes can result. 

Sure enough, when the 5016 silicon debugging reached Dave's origi- 
nal design intent, we began to see the telltale fingerprints of comparator 
memory. And not just your basic thermal-induced memory. These mem- 
ory symptoms disappeared at high temperature and were far worse at low 
temperature. Slowing down flie chip^s m^t^ clock provided alarmingly 
little benefit. Something strange was happening, and it surely wasn't 
modeled in SPICE. 

While Dave worked to characterize the problem on the 5016 probe 
station, I decided to build the NMOS differential amplifier shown in 
Figure 15-3. This decision was fortunate, because the ancient discrete 
MOSFETs I used (3N169s) had about 5 times the memory of Orbit 
Semiconductor's 3}mi MOSFETs. Simple Siliconix transmission gates 
moved the differential pair from huge overdrive to zero overdrive, and the 
results are shown in Figures 15-4 and 15-5. The MOSFET which carries 
the most current during overdrive experiences a temporary threshold volt- 
age increase. When the differential pair is returned to balance at the input, 
the output exhibits a nasty, long recovery tail. Soak the differential pair in 



Vdo=10V 



v. 




< Vbias 



Memory test circuit. 



255 



Moore's Law 




Rgure 15-4, 

Memory of nega- 
tive overdrive (V^ = 
5V,V^ = 3V). 



CLK1 5V/div 



Rgure 15-5, 

Memory of positive 
overdrive (V^ = 5V, 
V, = 7V). 




VouT 500»iV/div 



the overdriven state for 2x longer, and the lifetime of the recovery tail 
increases by L5x. Increase the magnitude of the overdrive beyond the 
point where all of the diffpair current is switched, and the shape of the tail 
stops changing. 

I figured that some sort of equilibrium between fixed charges and mo- 
bile charges at the Si-SiOj interface had to be involved. At high tempera- 
tures this equilibrium could be re-established in much less time than one 
comparison cycle, but at low temperatures recovery could be slow. Ever- 
longer "soak times" would allow ever-slower fixed-charge states to partic- 
ipate in the threshold shift. Since the fixed-charge population could never 
significantly reduce the mobile carrier population in the channel, satura- 
tion of the memory effect would occur once all of the mobile carriers 
were switched during overdrive. The story seemed to hang together. 

Well, venture-capital-funded startups don't survive based on stories, 
they survive based on fixes. You might not believe me if 1 told you what I 
was doing when I came up with the fix, but rest assured I wasn't pushing 
buttons on a workstation! Anyway, I guessed that if I could accumulate 
the surfaces of the diffpair MOSFETs, pull their channel voltages much 
higher than their gates, then I could change the hole concentrations at 
their Si-Si02 interfaces by maybe eighteen orders of magnitude, and 



CLK1 5V/div 




VouT 500^V/div 



Eric Swan$on 



M)o=10V 



CLXl 



^2- — °L 

SW1 r 




Figure 15-6. 

Erasure test circuit. 



erase that memory. The next day I built the circuit of Figure 15-^ and 
used it to produce the photographs of Figures 15-7 and 15-8. Only a few 
nanoseconds of flush time were required to completely erase the differen- 
tial pair's memory. It may seem like a strange thing to do to a precision 
comparator, but we've shipped a lot of product with flushed MOSFETs, 



CLK1 5V/div 



CLK2 5V/dlv 




Figure 15-7. 

Erased negative 
overdrive (V, = 5V, 
V£ = 3V). 



VouT 500MV/div 



Moore's Law 



CLK2 SV/div 



CLK1 5V/div 




VouT SOOfiV/dlv 



Figure 15-8. 

Erased positive 
overdrive (V^ = 5V, 



Sampling the Input 



When I interviewed at Crystal Semiconductor in 1984, 1 thought that self- 
calibration was the greatest thing since sliced bread and that customers 
would love it. Wrong. Customers loved the accuracy of calibrated parts, 
but they hated to calibrate to get it. If I had been managing the 5016 devel- 
opment, I wouldn't have paid much attention to post-calibration tempera- 
mre and power-supply shifts. Now I know better The true quality of a 
self-calibrated design is best measured by how stable its performance is 
without necalibration. Fortunately, Dave Welland was way ahead of me 
there. 

A conceptual view of the 5016 sampling path appears in Figure 1 5-9. 
The comparator input stage is used as part of an op amp during signal 
acquisition. This neatly autozeroes the stage's 1/f noise when we use it 
during conversion. Dave recognized that the chaige injection of the sam- 
pling switch adds error charge to the signal charge, and he minimized the 
error in an ingenious way. Rather than using a conventional transmission 
gate, Dave built a tri-state output stage into the closed- loop sampling 



Rgure 15-9. 

CS501 6 sampling 
architecture. 



Sampling 

Switch 
— ^ex- 



Analog 







Closed 

Imp 
Stage 



CDAC 



Gain 




>OUT 



Comparator 



288 



Eric SwanstHi 



To DAC 
Switches 



CDAC 

Hf- 



Stage 
Input 



>- 



H 



T 



T 



Figure 15-10, 
CS501 6 sampling 
switch detail. 



T = TRACK 
H = HOLD 



H 



path. A simplified schematic is shown in Figure 1 5-10. The gate voltage 
swings on the sampling devices are much smaller than those associated 
with transmission gates, and the swings can be designed to be power- 
supply imiependent Furthermore, at shutofF, most of the channel charge 
of the active-region sampling MOSFETs flows out their sources and away 
from CDAC. The results speak for themselves: the 501 6's offset shifts 
with temperature by less than .02LSB/°C. 

More recently, the progress in open-loop samplmg has been amazing. 
Just about every commercial delta-sigma converter samples its analog 
input with simple capacitor-transmission-gate structures. These open-loop 
sample-holds help achieve overall converter Imearities now surpassing 
120dB.' Optimization of sampling circuit performance only involves a 
few dozen transistors, and we're getting better all the time! Charge injec- 
tion from the MOSFET is getting pretty well understood, but newcomers 
should be forewarned that little of this understanding comes from the 
Sparcstation! 



Elegmee at a Higher Level 

The real elegance of analog VLSI circuits occurs beyond the subcircuit 
level. Successful analog VLSI architectures trivialize all but a few of a 
chip's analog subcircuits. Successful architectures are minimally analog, 
Successful architects know digital signal processing. Analog VLSI cir- 
cuits may be complex beasts, but when an architecture is really clean, 
you know. Your competition knows, too, a few years down the road! 



259 



Digital Signat Processing 



The journey was hectic but fun. Active-RC filters gave way to integrated 
switched-capacitor filters. The switched-capacitor filters were noisy 
compared to their active-RC predecessors, but you caii't be expected 
to work miracles with a mere -lOOOpF of total capacitance! Fortunately, 
switched-capacitor filter characteristics stayed put, allowing them to dom- 
inate sensitivity-critical, noise-tolerant telecom applicMicHis. 

Once Moore's Law gave us cheap enough digital transistors and cheap 
enough data converters, the switched-capacitor technology was doomed. 
Digital filters of wonderful precision have no sensitivity and no drift. 
Their noise performance can be perfectly simulated, and you can ask all 
the essential questions before silicon tapes out. Digital filters can be 
tested with digital test vectors to quality levels unheard of in the analog 
world. Analog chauvinists take heed: don't fight if you can't win. 

Fortunately for us dinosaurs, analog design experience helps produce 
better digital filters. Optimizing datapath wordwidths is very similar to 
optimizing kT/C noise. Quantizing filter coefficients is sinalar to quantiz- 
ing signals. Elegant, high-performance analog filter designs will always 
be difficult to put into production, but once an elegant DSP design is 
done, it's out of design forever. You can't beat that! 

The power of digital signal processing is never more apparent tixan 
when you're dealing with adaptive signal processing. Ad^^tive digital 
filters, be they echo cancelers or data channel equalizers, are simply more 
intelligent, more interesting, than their fixed-function predecessors. Take 
the time to understand them, and you' 11 be hooked. 

Norse and Robustn^s 

Just about everyone who transmits digital bits tries to send those bits as 
far as possible, as fast as possible, down the cheapest possible medium, 
until recovery of those bits is an analog problem* Digital data detection is 
one of the best long-term analog businesses there is. I'll add that nobody 
is too enthusiastic about sending a clock alongside the data. Thus, timing 
recovery is another of the great long-term analog businesses. 

Data detection and timing recovery circuits were among the first to 
embrace Moore's Law. Adaptive equalizers routinely clean up the fre- 
quency responses of real-world data channels. Maximum-likelihood 
receivers figure out the most likely transmitted sequence despite a chan- 
nel's additive noise. Error-correcting codes operate on the detected bit 
sequence, often providing further orders-of-magnitude improvement in 
system bit error rates. All of these techniques, originally perfected for 
board-level designs, are found in abundance on today's AVLSI chips. 



Traditional analog signal processing carries with it a certain hopeless- 
ness with respect to noise. As analog processing complexity grows, addi- 
tive noise sources grow in number, and system perftMtnsuice fades away. 
Modem digital communication system designers must be forgiven if they 
look at the weapons of the analog world and see Stone Age technology in 
the Iron Age. Throwing rocks may still get the job done, but the weapons 
of Moore's Law are elegant at a higher level. 

The Elepfiee of D^t Audio 

Audio data converters represent highly refined combinations of analog 
and digital signal processing. Converter performance now surpasses what 
reasoiiable people can claim to hear, and still it improves by 2dB/year. 
Can this possibly make sense? 

We all know that the great musical performances of our parents' gener- 
ation are irrevocably lost Lost by the limitations of recording electronics 
of that era. Lost thaiiks to the deterioration of analog st(Mrage media. Lost 
for a variety of technological reasons, but lost. Digital recording and stor- 
age now rule. The great sounds of our generation will never be lost. The 
job is not finished. Combine a small array of microphones, very good 
an^g-to-digital converters, and digital signal processing, and the results 
can be magic. We'll be able to hsten in new ways, to hear the contribu- 
tions of individuals to the sounds of their orchestras. 

R^rence 

I. Don Kerth et al., "A 120dB Linear Switched-Capacitor Delta-Sigma Modulator" 
ISSCC Digest of Technical Papers (February 1994). 



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JohnWitiison 



16. Anak^ Circuit Design 



Analog circuit design involves a strange mix of intuition, experience, 
analysis, and luck. One of the nicest things about the job is that you feel 
very smart when you make something work very well 

A necessary condition for being a good analog designer is that you 
know about 57 important facts. If you know these 57 important facts, and 
know them well enough that they become part of your working intuition, 
you may become a good analog circuit designer. 

Undoubtedly, there is an organized way to present these facts to the 
"interested student." The facts could be prioritized, or they could be alpha- 
betized, or derived from first principles. The priority could be assigned, 
with the most important facts coming first on the list (for emphasis) or last 
on the list (for suspense). Some day, when I have a lot of time, I'm going 
to put the list in the right order. 

It is difficult to present all the facts in such a way that will make sense 
to everyone. Sometimes I think that the only way to do this is by working 
examples over a twenty-year period. But we don't have time for that, and 
so as a poor alternative, I'm just going to write the facts down as they 
occur to me. There is a very good chance that you have run into most of 
these facts already. If so, just take heart that someone else has been tor- 
mented by the same problems. 

Here's the list of things you should know: 

0. If you even look at another engineer's approach to solving an 
analog circuit design problem before you solve the problem yourself, you 
greatly reduce the chance that you will do something creative. 

1 . Capacitors and resistors have parasitic inductance. A good rule 
of thumb is 4nH for a leaded component, and about 0.4nH for a surface- 
mount chip component. This means that a lOOpF leaded capacitor will 
have a self-resonance at 250MHz. This can be just great, if you are using 
the part to bypass a 250MHz signal, but might be a nuisance otherwise. 

2. If you don't want a transistor with a high bandwidth to oscillate in 
a circuit, place lossy components in at least two out of its three leads. A 
33Ci resistor in the base and collector leads will usually do the trfck with- 
out degrading performance. Fmite beads in the leads work well to fix the 
same problem. 



263 



Analog Circuit Design 



3. If you are probing a circuit with a dc voltmeter and the readings 
are not making any sense (for example, if there is a large offset at the 
input to an op anap, but the output is not pinned) suspect that somediing 
is oscillating. 

4. Op amps will often oscillate when driving capaeitive loads. A 
good way to think about this problem is that the low-pass filter formed by 
the output resistance of the op amp together with the capacitance ot the 
load is adding enough phase shift (taken together with the ph^e dllft 
through the op amp) that your negative feedback has become positive 
feedback. 

5. The base-emitter voltage (V^^) of a small signal transistor is about 
0.65V and drops by about 2mV/°C. Yes, the V^e goes down as the tem- 
perature goes up. 

6. TTie Johnson noise of a resistor is about 0.13nv/ ^}Hz^|Q. So, mul- 
tiply 0.1 3nV by the square root of the resistance value (in Ohms) to find 
the noise in a IHz bandwidth. Then multiply by the square root of your 
bandwidth (in Hertz) to find the total noise voltage. This is the rms noise 
voltage: you can expect about 5-6 times the rms value in a peak-to-peak 
measurement. 

Example: a Ikil resistor has about 4.1nV/'\/Hz, or about 41m 
Vrms in a l OOMHz bandwidth, which would look like about 0.2mV 
peak-to-peak on a lOOMHz 'scope. Note that the Johnson noise voltage 
goes up with the square root of the resistance. 

7. The Johnson noise current of a resistor is equal to the Johnson 
noise voltage divided by the resistance. (Thanks to Professor Ohm.) Note 
that the Johnson noise current goes down as the resistance goes up. 

8. The impedance looking into the emitter of a transistor at room 
temperature is 26CI divided by the emitter current in mA. 

9. All amplifiers are differential, i.e., they are referenced to a 
"ground" somewhere. Single-ended designs just ignore that fact, and 
pretend (sometimes to a good approximation) that the signal ground is 
the same as the ground that is used for the feedback network or for the 
non-inverting input to the op amp. 

10. A typical metal film resistor has a totiperature coefficient of about 
100 ppm/X. Tempcos about lOx better are available at reasonable cost, 
but you will pay a lot for tempcos around a few ppm. 

1 1 . The input noise voltage of a very quiet op amp is 1 n v/ Viiz. But 
there are a lot of op amps around with 20 nV/ VHz of input noise. 

Also, watch out for input noise current: multiply the input noise current 
by the source impedance of the networks connected to the op amp's in- 
puts to determine which noise source is most important, and select 



264 



your op amps accordingly. Generally speaking, op amps with bipolar 
front-ends have lower voltage noise and higher current noise than op 
amps with PET fixmt-ends. 

1 2. Be aware that using an LC circuit as a power supply filter can 
actu#y timlti^ tl^ power sui)i>ly noise ^th&t0sonm^fm^imi(^ of 
the filter. A choke is an inductor with a very low Q to avoid just this 

problem. 

1 3. Use comparators for comparing, and op amps for amplifying, and 
don't even think about mixing the two. 

14. Ceramic capacitors with any dielectric other than NPO should be 
used only for bypass applications. For example, Z5U dielectrics exhibit a 
capacitance change of 50% between 25°C and 80''C, and X7R dielectrics 
change their capacity by about 1 between 0 and 5V. Imagine the 

distortion! 

15. An N-channel enhancement-mode FET is a part that needs a posi- 
tive voltage (HI the gate relative to the source to conduct from drain to 

source. 

16. Small-signal JFETs are often characterized by extremely low gate 
currents, and so work very well as low-leakage diodes (connect the drain 
and source together). Use them in log current- to- voltage converters and 
for low-leak£^e input protection. 

17. If you want to low-pass filter a signal, use a Bessel (or phase lin- 
ear) filter for the least overshoot in the time domain, and use a Cauer (or 
elliptic) filter for the fastest rolloff in the frequency domain. The rise time 
for a Bessel-filtered signal will be .35 divided by the 3dB bandwidth of 
the filter. Good 'scope front-ends behave like Bessel filters, and so a 
350MHz 'scope will exhibit a 1.0ns rise time for an infinitely fast input 
step. 

18. A decibel (dB) is always 10 times the log of the ratio of two pow- 
ers. Period. Sometimes the power is proportional to the square of the 
voltage or current. In these cases you may want to use a formula with a 
twenty in it, but I didn't want to confuse anybody here. 

19. At low frequencies, the current in the collector of a transistor is in 
phase with the current applied to the base. At high frequencies, the col- 
lector current lags by 90'^. You will not understand any high-frequency 
oscillator circuits until you appreciate this simple fact. 

20. The most common glass-epoxy PCB material (FR-4) has a dielec- 
tric constant of about 4.3. To build a trace with a characteristic imped- 
ance of 1(X)Q, use a trace width of about 0.4 times the thickness of the 
FR-4 with a ground plane on the other side. To make a 50Q trace, you 
will need a trace width about 2.0 times the thickness of the FR-4. 



Analog Circuit Design 

21 . If you need a programmable dynamic current source, find out 
about operational transconductance amplifiers. NSC makes a nice one 
called the LM13600. Most of the problem is figuring out when you need 
a programmable dynamic current source. 

22. An 5 V relay coil can be driven very nicely by a CMOS output 
with an emitter follower. Usually 5V relays have a *'must make'' specifi- 
cation of 3.5V, so this configuration will save power and does not require 
any flyback components. 

23. A typical thermocouple potential is 30|iV/°C. If you caiie aijout a 
few hundred microvolts in a circuit, you will need to take care: route all 
your signals differentially, along the same path, and avoid temperature 
gradients. DPDT latching relays work well for multiplexing signals in 
these applications as they do not heat up, thus avoiding large temperature 
gradients, which could generate offsets even when the signals are routed 
differentially. 

24. You should be bothered by a design which looks messy, cluttered, 
or indirect. This uncomfortable feeling is one of the few indications you 
have to know that there is a better way. 

25. If you have not already done so, buy 100 pieces of each 5%, KW 
carbon film resistor value and arrange them in some nice slide-out plastic 
drawers. When you are feeling extravagant, do the same for the 1% metal 

film types. 

26. Avoid drawing any current from the wiper of a potentiometer. The 
resistance of the wiper contact will cause problems (local heating, noise, 
offsets, etc.) if you do. 

27. Most digital phase detectors have a deadband, i.e., the analog 
output does not change over a small range near where the two inputs are 
coincident. This often-ignored fact has helped to create some very noisy 
PLLs. 

28. The phase noise of a phase-locked VCO will be at least 6dB 
worse than the phase noise of the divided reference for each octave be- 
tween the comparison frequency and the VCO output frequency. Hint: 
avoid low-comparison frequencies. 

29. For very low distortion, the drains (or collectors, as the case may 
be) of a differential amplifier's front-end should be bootsttai^d to the 
source (or emitter) so that the voltages on the part are not modulated by 
the input signal. 

30. If your design uses a $3 op amp, and if you are going to be mak- 
ing a thousand of them, realize that you have just spent $3000. Are you 
smart enough to figure out how to use a $.30 op amp instead? If you 
think you are, then the return on your time is pretty good. 



«6 



31 . Often, the Q of an LC tank circuit is dominated by losses in the 
inductor, which are modeled by a series resistance, R. The Q of such a 
part is given by Q = 0)L/R. 

At the resonant frequency, f = i/2)cVlC, the reactance of the L and C 
cancel ejich other. At this frequency, the impedance of a series LC circuit 
is just R, and the impedance across a parallel LC tank is Q^R. 

32. Leakage currents get a factor of 2 worse for every lO'^C increase 
in temperature. 

33. When the inputs to most JFET op amps exceed the common- 
mode range for the part, the output may reverse polarity. This artifact 
wilt haunt the designers of these parts for the rest of their lives, as it 
should. In the meantime* you need to be very careful when designing 
circuits with these parts; a benign-looking unity follower inside a feed- 
back loop can cause the loop to lock up forever if the common-mode in- 
put to the op amps is exceeded. 

34. Und^r$tand the difference between "make-before-break" and 
"break-before-make" when you specify switches. 

35. Three- terminal voltage regulators in TO220 packages are wonder- 
ful parts and you should use a lot of them. They are cheap, rugged, ther- 
mally protected, and very versatile. Besides their recommended use as 
voltage regulators, they may be used in heater circuits, battery chargers, 
or virtually any place where you would like a protected power transistor. 

36. If you need to makeareally fast edge, like under lOOpS, use a 
step recovery diode. To generate a fast edge, you start by passing a cur- 
rent in the forward direction, then quickly (in under a few nanoseconds) 
reverse the current through the diode. Like most diodes, the SRD will 
conduct current in the reverse direction for a time called the reverse re- 
covery time, and then it will stop conducting very abruptly (a "step" re- 
covery). The ti*ansition time can be as short as 35pS, and this will be the 
rise time of the current step into your load, 

VkfeU, there you have it. These are the first 37 of the 57 facts you must 
know to become an analog circuit designer, I have either misplaced, for- 
gotten* or have yet to learn the 20 missing items. If you find any, would 
you let me know? Happy hunting ! 



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Jim Williams 



17. There's No Place Like Home 



What's your choice for the single best aid to an interesting and productive 
circuit design career? A PhD? An IQ of 250? A CAD workstation? Get- 
ting a paper into the SoHd State Circuit Conference? Befriending the 
boss? I suppose all of these are of some value, but none even comes close 
to something else. In fact, their combined benefit isn't worth a fraction 
of the something else. This something else even has potential economic 
rewards. What is this wondrous thing that outshines all the other candi- 
dates? It is, simply, a laboratory in your home. The enormous productiv- 
ity advantage provided by a home lab is unmatched by anything I am 
familiar with. As for economic benefits, no stock tip, no real estate deal, 
no raise, no nothing can match the long term investment yield a home lab 
can produce. The laboratory is, after all, an investment in yourself. It is an 
almost unfair advantage. 

The magic of a home lab is that it effectively creates time. Over the last 
20 years I estimate that about 90% of my work output has occurred in a 
home lab. The ability to grab a few hours here and there combined with 
occasional marathon 5-20 hour sessions produces a huge accumulated 
time benefit. Perhaps more importantly, the time generated is highly lev- 
eraged. An hour in the lab at home is worth a day at work. 

A lot of work time is spent on unplanned and parasitic activities. Phone 
calls, interruptions, meetings, and just plain gossiping eat up obscene 
amounts of time. While these events may ultimately contribute towards 
good circuits, they do so in a very oblique way. Worse yet, they rob psy- 
chological momentum, breaking up design time into chunks instead of 
allowing continuous periods of concentration. When I'm at work I do my 
job. When I'm at home in the lab is where the boss and stockholders get 
what they paid for. It sounds absurd, but I have sat in meetings praying for 
6 o'clock to come so I can go home and get to work. The uninterrupted 
time in a home lab permits persistence, one of the most powerful tools a 
designer has. 

I favor long, uninterrupted lab sessions of at least 5 to 10 hours, but 
family time won't always allow this. However, I can almost always get 
in two to four hours per day. Few things can match the convenience and 
efficiency of getting an idea while washing dishes or putting my son to 
sleep and being able to breadboard it now. The easy and instant availabil- 
ity of lab time makes even small amounts of time practical. Because no 



269 




Figure 17-1. 

Everything is undis- 
turbed and just as 
youliBflit,You can 
get right to wortc 



one else uses your lab» everything is undisturbed and just as you left it 
after the last session. Nothing is missing or broken,* and all test equip- 
ment is familiar. You can get right to work. 

Measured over months, these small sessions produce spectacular gains 
in work output. The less frequent but more lengthy sessions contribute 
still more. 

Analog circuits have some peculiar and highly desirable characteristics 
which are in concert with all this. They are small in scale. An analog de- 
sign is almost always easily and quickly built on a small piece of copper- 
clad board. This board is readily shuttled between home and work, 
permitting continuous design activity at both locations.^ A second useful 
characteristic is that most analog circuit development does not require the 
most sophisticated or modem test equipment. This, combined with test 
equipment's extremely rapid depreciation rate, has broad implications for 
home lab financing. The ready availability of high-quality used test equip- 
ment is the key to an affordable home lab. Clearly, serious circuit design 
requires high performance instrumentation. The saving grace is that this 
equipment can be five, twenty, or even thirty years old and still easily 
meet measurement requirements. The fundamental measurement perfor- 



1 . It is illuminating to consider that the average lifctiroc of an oscilloscope probe in a corporate 
tab is about a year. The company money and time lost due to this is incalculable. In 20 years 
of maintaining a home lab I have never broken a probe or lost its accessories. When personal 
money and time am at risk, things just seem to last longer. 

2. An extreme variant related to this is reported by Steve Pietkicwtcz of Linear Technology 
Cofporaiion. Faced with a one-week business trip« he packed a complete portable lab and buiU 
and debugged a 15-bit A-D converter in hotel rooms. 



mance of test equipment has not really changed much. Modem equipment 
simplifies the measurement process, offers computational capability, 
lower parts count, smaller size, and cost advantages (for new purchases). 
It is still vastly more expensive than used instrumentation. A Tektronix 
454 150MHz portable oscilloscope is freely available on the surplus mar- 
ket for about $150.00. A new oscilloscope of equivalent capability costs at 
least ten times this price. 

Older equipment offers another subtle economic advantage. It is far 
easier to repair than modem instruments. Discrete circuitry and standard- 
product ICs ease servicing and parts replacement problems. Contempor- 
ary processor-driven instruments are difficult to fix because their software 
control is "invisible,'' often convoluted, and almost impervious to stan- 
dard troubleshooting techniques. Accurate diagnosis based on symptoms 
is extremely difficult. Special test equipment and fixtures are usually re- 
quired. Additionally, the widespread usage of custom ICs presents a for- 
midable barrier to home repair. Manufacturers will, of course, service 
their products, but costs are too high for home lab budgets. Modem, com- 
putationally based equipment using custom ICs makes perfect sense in a 
corporate setting where economic realities are very different. The time 
and dollar costs associated with using and maintaining older equipment 
in an industrial setting are prohibitive. This is diametrically opposed to 
home lab economics, and a prime reason why test equipment depreciates 
so rapidly. 

The particular requirements of analog design combined with this set of 
anomalies sets guidelines for home lab purchases.^ In general, instmments 
designed between about 1965 and 1980 meet most of the discussed crite- 
ria. Everybody has their own opinions and prejudices about instmments. 
Here are some of mine. 

Oscilloscopes 

The oscilloscope is probably the most important instmment in the analog 
laboratory, Tektronix oscilloscopes manufactured between 1964 and 1969 
are my favorites. Brilliantly conceived and stunning in their execution, 
they define excellence. These instmments were designed and manufac- 
tured under unique circumstances. It is unlikely that test equipment will 
ever again be built to such uncompromising standards. Types 547 and 556 
are magnificent machines, built to last forever, easily maintained, and 
almost a privilege to own. The widely available plug-in vertical amplifiers 
provide broad measurement capability. The 1A4 four-trace and 1 A5 and 
1 A7A differential plug-ins are particularly useful. A 547 equipped with a 



3. An excellent publication for instrument shopping is "Nuts and Volts," headquartered in 
Corona, California. Telephone 800/783-4624. 



There's No Place Like Home 



1 A4 plug-in provides extensive triggering and display capability. The 
dual beam 556, equipped with two vertical plug-ins, is an oscilloscope 
driver's dream. These instiiiments can be purchased for less thaa the priee 
of a dinner for two in San Francisco."^ Their primary disadvantages are 
size and 50MHz bandwidth, although sampling plug-ins go out to IGHz. 

The Tektronix 453 and 454 portables extend bandwidth to 150MHz 
while cutting size down. The trade-off is lack of plug-in capability. The 
later (1972) Tektronix 485 portable has 350MHz bandwidth but uses cus- 
tom ICs, is not nearly as ruggedly built, and is very difficult to repair. 
Similarly, Tektronix 7000 series plug-in instruments (1970s and 80s) 
feature very high performance but have custom ICs and are not as well 
constructed as earlier types. They are also harder to fix. The price-risk- 
performance ratio is, however, becoming almost irresistible. A 500MHz 
7904 with plug-in amplifiers brings only $1000.00 today, and the price 
will continue to drop. 

Sampling 'scopes and plug-ins attain bandwidths into the GHz range at 
low cost. The Tektronix 661, equipped with a 4S2 plug-in, has 3.9GHz 
bandwidth, but costs under $100.00. The high bandwidths, sensitivity, 
and overload immunity of sampling instruments are attractive, but their 
wideband sections are tricky to maintain. 

Other 'scopes worthy of mention include the Hewlett-Packard 180 
series, featuring small size, plug-in capability and 250MHz bandwidth. 
HP also built the portable 1725 A, a 275MHz instrument with many good 
attributes. Both of these instruments utilize custom ICs and hybrids, rais- 
ing the maintenance cost risk factor. 

Related to oscilloscopes are curve tracers. No analog lab is complete 
without one of these. The Tektronix 575 is an excellent choice. It is the 
san^ size as older Tektronix lab 'scopes and is indispensable for device 
characterization. The more modem 576 is fully solid state, and has ex- 
tended capabilities and more features. A 576 is still reasonably expensive 
(»$ 1500.00), I winced when I finally bought one, but the pain fades 
quickly with use. A 575 is adequate; the 576 is the one you really want. 

Oscilloscopes require probes. There are so many kinds of probes and 
they are all so wonderful! I am a hopeless probe freak. It's too embarrass- 
ing to print how many probes I own. A good guideline is to purchase only 
high quality, name brand probes. There are a lot of subtleties involved in 
probe design and construction, particularly at high frequencies. Many off- 
brand types give very poor results. You will need a variety of Ix and lOx 
passive probes, as well as differential, high voltage, and other Q^es. 5012 
systems utilize special probes, which give exceptionally clem results at 
very high frequency. 



4. It is highly likely that Tektronix instruments manufactured between 1964 and 1969 would have 
appreciated at the same rate as, say, the Mercedes-Benz 300 SL . . . if oscilloscopes werr cars. 
They meet every criterion for collectible status except one; there is no market. As such, for the 
few aberrants interested, they are surely the world's greatest bargain, 



272 



Active probes are also a necessity. This category includes FET probes 
and current probes. FET probes provide low-capacitive loading at high 
frequency. The 230MHz Tektronix P-6045 is noteworthy because it is 
easy to repair compared to other FET probes. A special type of FET 
probe is the differential probe. These devices are basically two matched 
FET probes contained within a common probe housing. This probe liter- 
ally brings the advantages of a differential input oscilloscope to the circuit 
board. The Tektronix P6046 is excellent, and usually quite cheap because 
nobody knows what it is. Make sure it works when you buy it, because 
these probes are extraordinarily tricky to trim up for CMRR after repair. 
Finally, there are clip-on current probes. These are really a must, and the 
one to have is the DC-50MHz Tektronix P-6042. They are not difficult to 
fix, but the Hail effect-based sensor in the head is expensive. AC only 
clip-on probes are not as versatile, but are still useful. Tektronix has sev- 
eral versions, and the type 131 and 134 amplifiers extend probe capability 
and eliminate scale factor calculations. The Hewlett-Packard 428, essen- 
tially a DC only clip-on probe, features high accuracy over a 50mA to 10 
amp range. 




ITiere are never enough power supplies. For analog work, supplies should 
be metered, linear regulators with fully adjustable voltage output and 
current liniiting. The HP 6216 is small and serves well. At higher cur- 
rents (i.e., to 10 amps) the Lambda LK series are excellent. These SCR 
pre-regulated linear regulators are reasonably compact, very nigged, and 
handle any load I have ever seen without introducing odd dynamics. The 
SCR pre-regulator permits high power over a wide output voltage range 
with the low noise characteristics of a linear regulator. 

Signal Sources 

A lab needs a variety of signal sources. The Hewlett-Packard 200 series 
sine wave oscillators are excellent, cheap, and easily repaired. The later 
versions are solid state, and quite small. At high frequencies the HP 
8601 A sweep generator is a superb instrument, with fully settable and 
leveled output to lOOMHz. The small size, high performance, and versa- 
tility make this a very desirable instrument. It does, however, have a cou- 
ple of custom hybrid circuits, raising the cost-to-repair risk factor. 

Function generators are sometimes useful, and the old Wavetek 100 
series are easily found and repaired. Pulse generators are a must; the 
Datapulse 101 is my favorite. It is compact, fast, and has a full comple- 
ment of features. It has fully discrete construction and is easy to maintain. 
For high power output the HP214A is excellent, although not small. 



There's No Place Like Home 



Voltmeters 

DVMs are an area where Fm willing to risk on processor-driven equip- 
ment. The reason is that the cost is so low. The Fluke handheld DVMs are 
so cheap and work so well they are irresistible. There are some exception- 
ally good values in older DVMs too. The 5M digit Fluke 8800A is an ex- 
cellent choice, although lacking current ranges. The 4M digit HP3465 is 
also quite good, and has current ranges. AiK)ther older DVM worthy of 
mention is the Data Precision 245-248 series. These full featured 4J4 digit 
meters are very small, and usually sell for next to nothing. Their construc- 
tion is acceptable, although their compactness sometimes makes rqiair 
challenging. 

AC wideband true RMS voltmeters utilize thermal converters. These 
are special purpose instruments, but when you must measure RMS they 
are indispensable. The metered Hewlett-Packard 3400A has been made 
for years, and is easy to get. This instrument gives good accuracy to 
lOMHz. All 3400s look the same, but the design has been periodically 
updated. If possible, avoid the photochopped version in favor of the later 
models. The HP3403C goes out to lOOMHz, has higher accuracy, and an 
autoranging digital display. This is an exotic, highly desirable machine. 
It is also harder to find, more expensive, and not trivial to repair. 

Miscellaneous Instruments 

There are iiterally dozens of other instruments I have found useful and 
practical to own. Tektronix plug-in spectrum analyzers make sense once 
you commit to a 'scope mainframe. Types 1L5, ILIO, and 1L20 cover a 
wide frequency range, but are harder to use than modem instruments. 
Distortion analyzers are also useful. The HP334A is very good, and has 
about a .01% distortion floor. The HP339A goes down to about .002%, 
and has a built in low distortion oscillator. It is also considerably more 
expensive. Both are **auto-nulling*' types, which saves much knob twid- 
dling. Frequency counters are sometimes required, and the little HP5300 
series are very good general purpose units. The old 5245L is larger, but 
the extensive line of plug-ins makes this a very versatile instrument. 
Occasionally, a chart recorder makes sense, and the HP7000A (XY) and 
HP680 (strip) are excellent. The 7000A has particularly well thought out 
input ampHfiers and sweep capabilities. Other instruments finding occa- 
sional use are a variable voltage reference (the Fluke 332 is huge, but 
there is no substitute when you need it) and a picoammeter. Kiethley 
picoammeters (e.g., type 610) are relatively hard to find, but read into 
the femtoampere range. ''Diddle boxes" for both resistance and capaci- 
tance are very useful. These break down into precision and non-preci- 
sion types. General Radio and ESI built excellent precision types (e.g., 
G.R. 1400 Series), but many have been abused . . . look (and smell) in- 



274 



Jim Williams 



side before you buy. Non-precision types by EICO and Heathkit are 
everywhere, and cost essentially nothing. The precision variable air ca- 
pacitors built by General Radio (types 722D and the later 1422D) are 
particularly applicable for transducer simulation. They are also worth 
buying just to look at; it is hard to believe human beings could build 
anything so beautiful. 

Oscilloscope cameras are needed to document displays. Modem data 
recording techniques are relegating *scope cameras to almost antique 
status, which has happily depressed their price. My work involves a sig- 
nificant amount of waveform documentation, so I have quite a bit of spe- 
cialized cart^ra equipment. The Tektronix C-30 is a good general purpose 
camera which fits, via adapters, a wide variety of osciDoscopes. It is prob- 
ably the best choice for occasional work. The Tektronix C27 and C12 are 
larger cameras, designed for plug-in 'scopes. Their size is somewhat com- 
pensated by their ease of use. However, I do not recomnaend them unless 
you do a lot of photographic documentation, or require highly repeatable 
results. 

Finally, cables, connectors, and adapters are a must have. You need 
a wide variety of BNC, banana jack, and other terminator, connector, 
adapter, and cable hardware. This stuff is not cheap; in fact it is outrag- 
eously expensive, but there is no choice. You canH work without it and the 
people who make it know it. 

No discussion of a home laboratory is complete without comment on 
its location. You will spend many hours in this lab; it should be as com- 
fortable and pleasant a place as possible. The use of space, lighting, and 
furnishings should be quite carefully considered. My lab is in a large 



R9111VI7-2. 

You wilt spend 
many hours in this 
lab. It should be a 
comfortable and 
pleasant place. 





Tliere's No Place Like Home 




Rgure17-1 

Maintaining lab 
organization is 
parnful. but 
increases time 
efficiency. 



room on the second floor, overlooking a very quiet park. It is a bright, 
colorful room. Some of my favorite pictures and art are on the walls, and 
I try to keep the place fairly clean, In short, I do what I can to promote an 
environment conducive to working. 

Over the last 20 years I have found a home lab the best career friend 
imaginable. It provides a time efficiency advantage that is almost unfair, 
More importantly* it has insured that my vocation and hobby remain hap- 
pily and completely mixed. That room on the second floor maintains my 
enthusiasm. Engineering looks like as good a career choice at 45 as it did 
at 8 years old. To get that from a room full of old equipment has got to be 
the world*s best bargain. 



Jim Williams 




Figure 17-4. 

Ifs convenient to 
be able to write up 
iab results as they 
occur. 



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Barrie Gilbert 



1 8. It Starts with Tomorrow 



Fostering Innovation in the Chip Biz 

What are the roots of innovation? How does it actually happen in the 
microelectronics industry today? How can it be fostered and enhanced? 
These are questions of considerable interest to managers. It is suggested 
here that innovation is a very personal process, beginning with a strong in- 
terest in tomorrow's needs and the visuaUzation of significantly different 
solutions. Modem management methods aimed at enhancing the rate and 
quality of innovative product design may fail because they depend too 
much on what are essentially algorithmic approaches to group improve- 
ment, with diminished emphasis on the need to recognize, encourage and 
support the singular vision. A recurrent theme in today's corporations is 
that new product concepts must be firmly — ^perhaps even exclusively — 
based on marketing data acquired through listening to the "Voice of the 
Customer." While recognizing the critical role and immense value of 
market research, this view is thought to be an incomplete and inadequate 
characterization of the fundamental challenge, which requires a stronger 
emphasis on the role of anticipation in product innovation, stemming both 
from a broad general knowledge of the traditional marketplace and a high- 
spirited sense of tomorrow's needs before these are articulated. 

"I do not think there is any thrill that can go through the human 
heart like that felt by the inventor as he sees some creation of the 
brain unfolding to success . . . Such emotions make a man forget 
food, sleep, friends, love, everything . . 

— NIKOLA TESLA, 1896 

Innovation! A high-spirited word, much in evidence in today's techno- 
logical world. Though not a unique twentieth-century phenomenon, the 
relentless introduction of ever more innovative products has become a 
particularly evident, in fact, a characteristic aspect of modem techno-cul- 
tures. In some industries, where product life-cycles are short, achieving a 
high rate of innovation is a key strategic objective. Nowhere is this depen- 
dence on focused, purposeful innovation of the highest quality more appar- 
ent than in the microelectronics business. But what are the fundamental 



279 



It starts with Tomorrow 



sources of the innovative spark? What distinguishes innovative products 
from effective and adequate — but totally predictable — ^foUow-ons and 
spin-offs? What separates creative flair from routine incrementalism? 
What can be done to encourage innovation and elevate the output of finely 
wrought, ground-breaking, universally acclaimed products in a modem 
high-tech company? 

This essay expresses my personal views about how innovation really 
happens, in contrast to how it might be thought to happen, in a modem 
company. These opinions are based on forty years of plying my trade as a 
designer of electronic devices, circuits, and systems. Longevity of service 
brings no guarantees of wisdom. However, it may perhaps help one to see 
the field with a reasonably broad perspective and to address contemporary 
issues of managing innovation possessed of some familiarity with tiie 
overall challenge. Because it is a personal position, it may be useful to 
begin with a sketch of my early years. 

I lost my father in World War II, a blow I've never been able to quan- 
tify. He was a classical pianist; had he lived, I no doubt would have pur- 
sued my own love of serious music full-time. Instead, I settled on radio 
and chemistry as hobbies, partly influenced by my much-senior brother, 
who had already made some receivers. I had an upstairs experiments 
room, fastidiously organized, in which I built many receivers and trans- 
mitters, using brass-and-ebony components from the earliest days of 
radio, screwed down on to soft-wood bases — the quintessential bread- 
board! Usually, there was a further bo^d screwed and angle-biacketed to 
provide a front panel, on which I mounted such things as input and out- 
put binding terminals, switches for range-changing, and mgged multi- 
vaned variable capacitors for tuning. I had begun with the obligatory 
'crystal set,* and progressed through one-valvers, several TRF receivers, 
and a seven- valve superhet that I designed from the ground up. Having 
no electricity in my home (it was lit by gas mantles, and heated in the 
winter by coal fire in just one room), all of my early experiments were 
battery powered, giving me a taste for the low-power challenge inherent 
in the design of contemporary integrated circuits! 

With the cessation of hostilities, a plethora of government-surplus elec- 
tronics equipment hit the market at incredible prices. Using money earned 
from a newspaper route, I purchased as much as I could afford. My 
bounty included exquisite VHP receivers, enigmatic IFF systems (sans 
detonator), A-scan and PPI radar 'indicators units* (one of which had two 
CRTs!), and some beautiful electromechanical servosy stems, whose os- 
cillatory hunting in search of a steady state was mesmerizing. This stuff 
was deeply alluring and bristling with possibilities. With these war-spared 
parts, I built my first clearly remembered oscilloscopes and a TV receiver, 
in 1949-50. It was the only TV on the block, and on it my fettiily and l 
watched the Grand Coronation of Elizabeth 11. 

These were profoundly joyous and fulfilling days of discovery. I recall 
the thrill of 'inventing' the super-regenerative receiver; the cross^coupled 
multivibrator (with triodes, of course, not transistors), voltage regulators. 



280 



pentode timebase generators, pulse-width modulation, AVC and AFC, 
electronic musical generators, and a good deal more, all out of a free- 
wheeling * what if?' approach to my hobby. I was hardly deflated to later 
learn that others had beaten me to the tape, often by several decades! The 
urge was always to pursue an original design, from ground zero, and to 
try to understand &e fundamentals. I occasionally bought magazines like 
Practical Wireless, but I couldn't inmgine actually building something 
from those pages! It was the same with model aircraft and boats: I'd much 
rather find out what worked and what didn't by direct experience (read 
failure) than hiild to somebody else's plans. Copying, even with the 
prospect of achieving superior performance, was no fun at all. 

I started my first job on a brisk, leaf-shedding autumn morning in Sep- 
tember 1954, at the Signals Research and Developn^nt Establishment 
( SRDE). The labs were a rambling group of low wooden buildings, care- 
fully secreted among trees and bristling with exotic antennas, perched 
atop chalk cliffs overlooking the English Channel. Oddly, it didn't seem 
like work^ at all: I was actually getting paid for cheerfully pursuing what 
I had passionately enjoyed doing since single-digit years, but with im- 
mensely augmented resources (the British Government!), The point- 
contact transistor was one of the new playthings in my lab. Six years later, 
at Mullard, I designed an all-transistorized sampling oscilloscope, and 
emigrated to the USA in 1964, to pursue 'scope design at Tektronix, in 
Oregon. 

There, during the late sixties, I was given considerable latitude — even 
encouragement— to develop novel semiconductor devices and circuits at 
Tek, My chosen emphasis was on high-frequency nonlinear circuits. Out 
of this period came monolithic mixers and multipliers, and the discovery 
of the generalized 'translinear-principle/ In 1972, back in England for a 
while, I worked as a Group Leader at the Plessey Research Labs, on opti- 
cal character recognition systems (using what nowadays would probably 
be called *neural network techniques,' but which I just called adaptive 
signal processing), optical holographic memories and various com- 
munications ICs. I was also writing a lot of software at that time, for 
simulating three-dimensional current-transport behavior in various 
'super-integrated' semiconductor structures, including carrier-domain 
multipliers, magnetometers, and a type of merged logic like PL. 

My relationship with Analog Devices goes back 22 years, fully half of 
my working life. While still with Plessey, I was contacted by Ray Stata. 
We discussed the idea of working for Analog Devices. I was unable to 
leave England at that time because my mother was seriously ill, so we 
worked out a deal, the result of which was that I *re-engineered' the two 
bedrooms on the top floor of my three-story house in Dorset, on the south 
coast of England, one into a well-equipped electronics lab (including an 
eariy-production Tektronix 7000-series 'scope I had helped design), the 
other into a library-quiet, carpeted, and cork-walled office, equipped with 
a large desk, overlooking Poole Harbor, and an even-larger drawing 
board. During this happy sojourn I designed several 'firsts' — the first 



It starts vrith Tomorrow 



complete IC multiplier designed for laser-trimming, the first monolithic 
RMS-DC converter, the first monolithic V/F converter with 0.01% linear- 
ity, the first dual two-quadrant multiplier, all of which I laid out myself, 
using mylar, pencils, and many, many erasers, the sort wrapped in a spiral 
paper sheath . 

The formal VOC emphasis was decades away. Yet these products were 
not conceived with total disregard for practical utility or market potency. 
Nor was the importance of listening to the customer an alien idea. Clear- 
ing out some old files recently, I was amused to find my thoughts about 
this in a memo written following a brainstorming session we had in 
November of 1975: 

"I would be in favor of having one engineer who spends more than 
h^f his time traveling around the country collecting in-deptti infor- 
mation, and whose responsibilities were to ensure that our current 
development program constantly matches the mood of the market- 
place . . . [and] be alert for important new opportunities. He would 
not function primarily as a salesman . . . [but] would carry a 
constantly-updated portfolio of applications material and would 
offer to work with the customer on particular requirements. This 
type of professional Unk is far more beneficial (both to m and the 
customer) than [excessive emphasis on the deliberations of product 
selection committees] and anyway will probably become essential 
as our products become more sophisticated." [Original underlining] 

The Wellsprings of Innovation 

I've always been interested in the process of innovation and its traveling 
companion, creativity. I'm curious about why and how it arises in one's 
own work and how it might be fostered in one's co-workers. At root, in- 
novation is a matter of matching the needs of the market — in all of its 
many facets and dimensions — ^to the ideas, materials, tools, and other 
constructive means at our disposal. Something, perhaps, that might best 
be entrusted to a team. There is no question that the sheer scale and com- 
plexity of many modem IC projects demand the use of teams, and that 
good team-building skills are an essential requirement of the effective 
engineering manager. Yet it seems to me that innovation remains a highly 
individual, at times even lonely, quest, and that enhancing one's own in- 
novative productivity — both in terms of quantity arid quality — -must al- 
ways be personal, not a group or corporate, challenge. 

Undoubtedly, the innovative spirit can be seriously hampered by a 
lack-luster infrastructure, run by senior managers who have their minds 
on higher things, and by executives who view their corporation as little 
more than a contract-winning and revenue-generating machine, to be 
optimized up by frequent rebuilding and generous oiling with business- 



282 



school dogmas. Conversely, the often frail, tenuous groping toward indi- 
vidually distinguished performance on the part of young designers can be 
transformed by a supportive corporation, one that has many erstwhile 
engineers at the top, which recognizes latent talent, and which is willing 
to take a gamble on the individual. I have worked under both regimes, and 
can truthfully say that at the Tektronix of the sixties and at Analog De- 
vices throughout its history, their top executives succeeded in fostering 
engineering excellence through the massive support of competent techni- 
cal contributors, and the thoughtful, attentive consideration and encour- 
agement of tt© idiosyncratic visions of such people. 

Innovative urges originate within the individual, and can be either 
quenched or fanned into a blaze by corporate attitudes. But where do the 
ideas come f mm in the first place? I like to say that "Innovation Starts 
with Tomorrow." It is the "Start of the Art" — the new art that will one day 
become commonplace, even classic. Prowling at the boundary between 
the present and the future, the innovator never ceases to peer through the 
cracks and holes in the construction fence for telltale signs of new oppor- 
tunities, as our world changes day by day. Innovation consists of this per- 
sistent, vigilant boundary watch followed by a creative response to what 
is seen. Essential precursors to innovation are a prolonged study of a cer- 
tain class of problems, a thorough familiarity with the field of application, 
and total immersion in the personal challenge of making a significant 
contribution to the state of the art. 

But is this enough? Many authors have grappled with the enigma of 
creativity. Some believe that it happens when normally disparate frames 
of reference suddenly merge in a moment of insight. For example, Arthur 
Koestler writes^ 

, . a familiar and unnoticed phenomenon ... is suddenly 
perceived at an unfamiliar and significant angle. Discovery often 
means simply the uncovering of something which has always been 
there but was hidden from the eye by the blinkers of habit." 

Instances of this type of discovery come to mind: Watt and the steam 
kettle (probably apocryphal); Fleming and penicillin; Archimedes and his 
tub; etc. But others, including myself, reject the widely held idea that 
radically creative concepts can arise from a methodical, conscious, logi- 
cal process. R B. Medawar, who won the Nobel Prize for Medicine in 
1960, believes^ that it is a matter of "hypothetico-deduction." He states 
that hypothesis generation is 

. , a creative act in the sense that it is the invention of a possible 
world, or a possible fragment of the world; experiments are then 



1 . Afthur Koestler, The Act of Creation: A Study of the Conscious and Unconscious in Science and 
Art (Hew Yoik: Deli Publishing Co., 1 967), 1 08. 

2. P. B. Medawar, The Art of the Soluble (London: Methuen & Co. Ltd., 1967), 89. 



It starts with Tomorrow 



done to find out whether the imagined world is, to a good enough 
approximation, the real one." [Italics mine] 

According to Medawar, the creative process begins with an act of imag- 
ination, more like an act of faith, without a strong factual basis; the testing 
of the hypothesis that follows, on the other hand, requires deduction, a 
quite different activity.^ Others, like Edward de Bono,^ believe in the simi- 
lar notion of "lateral thinking." In this scenario, one consciously jumps 
out of the familiar boundaries into a what-if world where the rules are 
different, establishes a workable staicture which is self-consistent within 
this temporary frame of reference, then seeks to re-establish connections 
with the 'real world.' I find this matches my mode of working very 
closely. 

I've got my own theory about the sources of the creative spark. I begin 
by noting that the most well-known aspect of the 'creative moment' is 
that it is mercurial and elusive. I suspect that human free will and creativ- 
ity both have a thermal basis. Minds are an epiphenomenon of their phys- 
ical substratum, the brain, which is diffused with thermal noise.^ In 
particular, large aggregations of neurons are subject to statistical fluctua- 
tions at their outputs, and almost certainly exhibit a chaotic aspect, in the 
formal sense. That is, a small incUnation on the part of just a single neu- 
ron to fire too soon, without *the right reason,' can trigger an avalanche in 
coupled neurons in the group, whose states may cluster around a neural 
'strange attraetor.' This microcosm gets presented to our conseiousness (a 
few milUseconds later) for consideration; we interpret it as that inexplica- 
ble, but very welcome, revelation. 

When this happens in its milder, everyday forms (such as choosing 
what to select from a lunch menu) we simply call it free will; when it 
happens while we're thinking about a problem (or maybe no/ thinking 
about the problem), and culminates in that felicitous, euphoric, amusinf 
'*Aha!" moment, then we give the name 'creativity' to this cerebral 
sparkling, and call the outcome a Startling New Idea; WbM^e each end 
up doing with these serendipitous sparks depends on our mood, on our 
orientation to opportunity, and on the strength we can draw from our in- 
terna 'databases.' For the innovator^ tfiese databases (rtmghly eipivS^nt 
to experience) would include such things as general and specific market 
knowledge, and familiarity with relevant technologies, and of what has 
been successfully done already ('prior art') in the form of circuit topolo- 
gies, IC products, and complete systems. Allowing these spmks fti& rem 
to control the immediate outcome, by inviting interaction with these data- 
bases and by suspending judgment, is essential to the creative process. 



3. "The Reith Lectures Are Discussed," The Listener (published by the British Broadcasting 
Corporation), (January 11 1968): 41. 

4. See, for example, "de Bono's Thinking Course," Facts on File Publications (1982). 

5. Viewed as an electrochemical entity, the neuron could be said to exhibit the ionic noise of a 
chemical reaction; but this, too, ultimately has a thermal basis. 



284 



Clearly, whatever is going on in the attic, we are not deterministic state 
machines, that, like computers, always deliver the same response for the 
same stimuli. Nor are all our conclusions reached dianoetically. It is for 
this reason that even the most advanced computers are so utterly boring 
and lacking in creative sparkle- On the other hand, even inexpensive 
home computers today are very, very good at retaining huge archives of 
knowledge, accessible within milliseconds, and are very, very good at 
carrying out difficult calculations, of the sort that 'radio engineers' up 
until the '70s would have to do by hand, or with the help of a 'slip stick' 
(for years, the primary icon of the engineering professions), wastefully 
consuming a large fraction of their working day. 

Computers, in this very limited sense, may have better 'experience' on 
which to draw than we have. But they are rule-based, and don't have our 
probabilistic sparkle (because we don't allow them to). The present sym- 
biosis between unruly human minds and cool-headed digital computers, 
who live by the rule, and who can reliably provide us, their users, with 
instant access to vast amounts of knowledge, has already transformed the 
process of innovation, although in a rather predictable fashion. An even 
stronger symbiosis will result, I believe, with the eventual installation of 
non-determinism in neural network-based thinking systems, perhaps in 
the next decade. This courageous step is destined to radically alter the 
way we will innovate in the future, with quite unpredictable conse- 
quences. I find this a fascinating prospect. 

ITie philosopher Jean-Francois Lyotard comments** 

'In what we call thinking the mind isn't 'directed' but suspended. 
You don't give it rules. You teach it to receive. You don't clear the 
ground to build unobstructed: you make a little clearing where the 
penumbra of an almost-given will be able to enter and modify its 

contour." 

This reference to the negative effects of 'direction' and 'rules' is 
telling. There is a tension that arises in a corporate environment between 
the need to have structure in certain cases and the need to leave other 
things unstructured. Innovation does not thrive in a rule-rich context; on 
the other hand, it can be significantly enhanced in a tool-rich context, 
particularly if these tools provide access to a large body of knowledge 
and allow one to play uncountable 'what-if ' games with this knowl- 
edge. Such tools have proven time and agam to provide profound and 
completely unexpected insights: the new world of fractals was unknown 
and probably unknowable without computers, and the same can be said 
of chaos theory, whole-body imaging, molecular engineering, and much 



6. J-F Lyotard, "The Inhsman: Reflectioiis on Time," tr. G. Bennington and R. Bowlby (Stanford: 
Stanford University Press, 1991): 19. 



H earts with Tomorrow 



else. Imaginative use of computers is nowadays almost synonymQUS 
with innovation, at least, in the way they open up our minds to visualiz- 
ing new possibilities. It remains up to us, though, to turn fragite, promis- 
ing ideas into robust, marketable products, which is the true essttfice of 
innovation. 

The precise moment when a new concept, or 'art,* first bem-s fruit is 
especially significant. Although always about ideas and personal insists, 
innovation is not so much about knowing how (that is, 'know-how' ) as 
about actually making things happen. It frequently involves recourse to 
the use of markedly unusual and unexpected methods in achieving its 
objeetives. And although we generally use the term innovation' in con- 
nection with practical advances, theory may play an important role in the 
process, and one can also innovate in a purely theoretical direction (for 
example, Norbert Wiener's seminal statistical theory of communication). 
But there always has to be a tangible product, usable by many others, as 
output. 

I've stressed that innovation — invention — is largely a matter of one's 
personal perceptions of, and responses to, one's surroundings. It arises 
out of seeing the myriad opportunities that abound in a utilitarian culture 
in an ever-fresh and bold new light. Opinions may differ, but I believe it's 
about being convinced first, of the validity of that singular vision, a bold 
assurance arising in equal measure from first, experience of what works 
combined with a firm grasp of the current needs of the market; and sec- 
ond, an awareness of the necessity to continually channel that vision into 
profitable realities. In managing our self-image, it's okay to appropriate to 
oneself such terms as product champion, conceptualizer, mentor, inventor, 
or master of the art, if we feel that truly describes what we are and what 
we do. It would, of course, be immodest to make those clmrm pi^lkfy 
about oneself. Nevertheless, these are the kinds of 'good words' strongly 
motivated achievers might well choose to describe their aspirations in 
private moments. It's okay to feel proud of one's best achievements, if 
they've proven market- worthy. 

Invention thrives in a multi-disciplinary mind. During the course of 
developing a new IC product, the well-equipped innovator will, over the 
course of a typical day, need to take on the mind of circuit designer (con- 
cerned with basic concepts and structure), technical writer (explaining 
one's work to other team members, or thinking about how the applica- 
tions are going to be presented), semiconductor device specialist (during 
transistor design for critical cells), marketeer (maintaining a focus on the 
needs of the customer, firming up the formal specs, continually verifying 
fitness of use, etc.), test engineer (in preparation for production), and 
accountant (watching die size, yield, cost). 

Innovative design is far removed from the serial, step-by-step process 
that is sometimes suggested. It is an extremely iterative, exploring, yearn- 
ing, and discovering process. Dissatisfaction abounds at every turn. 
Revisions occur with stunning regularity. One's attention is constantly 
readjusting, at every level. For example, during die design phase we need 



286 



to address numerous minor yet essential aspects of our circuit's behavior 
(say, stability with a nasty load); a few minutes later we may be attending 
to, say, optimizing a device geometry; sometimes tudcering at the input 
boundary, sometimes at output; checking temperature behavior again, 
then AC, then transient, then beta sensitivity, operation at the supply lim- 
its, and round and round again. Out of all this, the final solution gradually 
comes into sharper focus. 

Even while primarily in the 'design' mode, it may be hard to think 
about the product entirely as a challenge in circuit refinement. One needs 
to frequently pop out of the schematic view of 'reality* and briefly review, 
say, applications issues, trying on the shoes of the user again, to see how 
well they fit; a moment later, plunging back into schematicland, scrutiniz- 
ing the horizon one more time for things that maybe aren't yet quite right; 
or challenging oneself again about the justification for the overall archi- 
tecture, or the need to reconsider the practicality of the present chip 
structure, the roughed-out layout, and so on. The dynamics of 'getting 
it all together' involve a lot of judgment, art, trial and error, and are far 
removed from the popular image of the nerdy engineer, methodically 
pursuing serial, rule-based, 'scientific,' forward-pushing progress. Only 
the neophyte engineer remains in the same mode for hours, or even 
weeks, at a time. 

We need better tools. Faster simulation is always in demand. Certain 
aspects of circuit behavior — such as finding the IdB compression point of 
a mixer — need a lot of CPU time, and have to be performed in the back- 
ground, although it is often difficult to take the next step until such a re- 
sult is available. The simulation of other behavioral aspects may simply 
not be possible at all, or to the required accuracy, and one is left to devise 
ingenious analytical methods to solve such problems in the classical way, 
using circuit theory ! Though a well-understood challenge, the need for 
very rapid turn-around in a simulation context is rarely viewed as an es- 
sential aspect of the ergonomics of innovation. Fast machines don't just 
provide quick answers; they are better able to run beside us in a partner- 
ship. But we should be the gating factor; it should be our wits that limit 
the rate of progress, not those of an unresponsive machine. 

Modeling the Market 

Innovation in a large corporation depends on a lot more than our willing- 
ness to put the best of our personal insights and creative talents to work. 
We need to establish and maintain firm anchor-points in the marketplace, 
always the final arbiter of success and failure for the serious product de- 
signer. While our primary focus must be on the technical issues relating 
to the systems, components, and technologies that we and competing 
companies each develop, we must also thoroughly understand the dynam- 
ics and psychology of our particular industry. Further, we must under- 
stand not only our current maricets intimately, but go well beyond: we 



It starts wWi Tomorrow 



must constantly anticipate the future needs of these markets. As innova- 
tors, we must be neither overly timid, nor cocksure, ateut that challenge* 

If tiniid, we might fall into the trap of modeling this 'world of the mar- 
ket' as a fortress of rationality, where there are compelling reasons why 
our customers' preset solutions are not just satisfactory, but ifitimidat' 
ingly superior; a place where all the good ideas that relate to soiiae par- 
ticular business have long ago been figured out, and around which an 
impenetrable wall has been built. Such an apologetic approach to our 
domain of opportunity would be unwise. The truth is that the majority of 
users of advanced component and systems are daily managing to scrape 
by with barely adequate solutions to their technical problems, and are 
constantly on the lookout for more competitive, more reliable, more pow- 
erful alternatives. They crave to be advised by their vendors. With an eye 
on leadership, we shouldn't let them down. 

Yet we cannot afford to be too confident about our prowess to ser\'e the 
world of the market. In a 'good company,' with a trail of successes behind 
it, one may occasiGnally hear scornful comments about one's competitors. 
The innovative spirit has no place for either derision or complacency. 
One's view of the market and of one's competitors needs at all times 
to he honest focused, realistic, and balanced. In this outward-embracing 
view of our world, we must also include advanced ideas coming out of 
academia, the ideas of others in industry, as expressed in the profes- 
sional journals and at conferences and workshops, and the commen- 
taries of journalists writing about our business in the trade books and 
financial-world newspapers. In short, we need to be effective gatekeepers, 
balancing self-motivated innovation against careful reflection of external 
factors, the eager anticipation of the challenge against thoughtful assimi- 
lation. 

In our field of microelectronic product design, one innovator was both 
a legend and an enigma: this was Bob Widlar, who died in 1991 J Those 
who knew him recalled that he was very hard to relate to. Bob Dobkin, 
who worked alongside Widlar, said: "Widlar knew it all, he knew he 
knew it all and nobody else knew anything." He was a maverick and a 
nonconformist, with many stubborn ideas of his own. Yet he did amaz- 
ing things with silicon, and introduced many firsts: "He pioneered the 
three-terminal voltage regulator, on-chip power devices, the bandgap 
voltage regulator, super-beta transistors and a full bag of clever and inter- 
esting circuit and device techniques," said Jim Solomon. 

"One thing that everyone should know: Bob was concerned with all 
aspects of his craft (or art), including 'marketing,' in the true sense of 
understanding the economics and systems applications of his products " 
observes Analog's Lew Counts, who believes we would do well to replace 



7. I am grateful to Lew Counts for reminding me of the tribute written by Jim Solomon in the 
August 1991 issue of the IEEE Journal ofSolid-State Circuits, vol. 26, no. 8, pp. 1087'-1088, 



288 



some of the organizational paperwork currently on our desks with Bob's 
seminal articles. Although we may be disappointed to find nothing ex- 
plicit in them about his motivation for the development of a new IC, nev- 
ertheless his market orientation and his overall grasp of the possibilities 
of the medium were an ever-present and tangible aspect of his work. One 
wonders whether Bob Widlar would fare as well in modem corporations 
as he did at National Semi in the '60s, or what his reaction would be to 
some of the prevalent "improvement" methodologies. 

To a large extent, today's innovators rely on existing markets to guide 
their thinking. To what extent has it always been that way? How were 
innovators of long ago motivated? Was their way of creating new products 
applicable to us today, locked as we are in a co-dependent embrace with 
the customer? We engineers are inheritors of the spirit of a long lineage of 
innovators, and the beneficiaries of their ei^rgies. The golden braid of 
knowledge technologies^ can be threaded through The Sawy Sumerians 
(c. 3,000 BCE), Archimedes (287-212 BCE), Lenny da Vinci (1452- 
1519), Jack Gutenberg (?-1468), Bill Gilbert (1544-1603), Humpie Davy 
(1769-1830), Mike Faraday (1791-1867), Charlie Babbage (1791-1871), 
Sam Morse (1791-1872), Wem von Siemens (1816-1982), Jim Maxwell 
(i 831-1979), Tom Edison (1847-1931), Hank Hertz (1857-1894), Chuck 
Steinmetz (1865-1923), Nick Tesla (1856-1943), Guggi Marconi (1874- 
1 937), Norbert Wiener (1894^1964), Ed Armstrong (1890-1982), and 
many more. 

The key feature of the work of these giants of technology, and dozens 
more like them, is that they didn *t wait to be told to innovate. What they 
did stemmed from a fundamental urge to produce solutions that signifi- 
cantly challenged the norms, and could even transform the world. The 
Sumerians' insight that the physical tokens^ used to keep track of finan- 
cial transactions (and much else) could be replaced by distinctive marks 
on soft clay tablets, which were later transformed into records of archival 
quality by exposure to the noonday sun, was innovation springing from 
great independence of mind. (Who would have been the 'customer' for 
writing? The very thought is laughable.) 

Most of us feel (justifiably) that we cannot aspire to the greatness of 
such inventors, particularly in our limited, highly specific domain of 
virus-scale electronics. Nevertheless, it is proper- — and not immodest, in 
my view — ^to seek to emulate their example. Like them, we need to have a 
clear conception of what would be useful; to always be ready to propose 
solutions without first needing to be asked; to be confident and passion- 
ately committed to one's vocation; to maintain a high level of co«cm/m- 
tion\ to feel resourceful, capable, well-equipped, determined, to never 
cease devisii^ a string of self-imposed challenges for solution; to practice 



8. Which is what electronics is all about, in the final analysis. 

9 . See "Before Wtitittg: Vol 1 » From Countiiig to CuBciform " by Denize Schmandt-Besserat, 
University of Texas Ftes (1992) for an enlightening account of the precursors of writing. 



It Starts with Tomorrow 



persistence. It is out of these attitudes — ^the *state of the heart*— that the 
best innovation wells forth, 

UstentngtoVbices 

From the tastefully furnished executive wings of modem corporations we 
often hear that> unequivocally, the process of innovation must begin with 
the customer. It is said that product concepts must be founded directly on 
one*s intinmte underst^ttiding of e^h customer's needs, garr^ed through 
countless hours of listening attentively to what we are told is the Right 
Thing To Do. 

There is no denying the importance of paying close attention to our 
customers* needs — ^particularly when that means a large group of cus- 
tomers with similar needs. But is this the motive-force of innovation? 
Sometimes. An earnest and sincere involvement with the customer is 
frequently important — even essential — bright from the start, and skillful 
probing may well lead to valuable and unexpected insights, which need 
our careful assessment before a new development is started. Usually, 
though, the rea/ * start of the art' is quite fuzzy. Many valuable product 
ideas reach right back into our early fragmentary awareness of the general 
needs of an emerging market, with roots in our broad knowledge of prac- 
tices and trends. The final design will invariably be based as much on our 
own stored ideas about critical requirements and specifications for prod- 
ucts in the customer's field of business, and techniques to address those 
needs, which we've painstakingly garnered over a long period of time, 
as it is on the customer's voice, attended to for a few short hours. 

Often, that costly trip to the customer is not so much to fuel the inno- 
vative process as to establish the realism and scale of the business oppor- 
tunity, the volumes, pricing and schedule, information on which to base 
decisions about multiple-project resourcing. Although we will be very 
attentive to what the customer may tell us about technical matters, it is 
unusual that something is learned about the function or specifications that 
is completely unfamiliar. 

This is particularly true of mature generic products (such as most £ub- 
plifiers) and of many application-specific ICs (ASICs) and other special- 
purpose products that address well-developed markets. The success of 
new types of product, and user-specific ICs (USICs), having hitherto un- 
available (or even unattainable) fiinctions, depends very heavily on meet- 
ing an 'external' set of requirements down to the letter, and obviously 
requires much more careful listening. On occasions, though, even these 
don't get completely defined by a customer, but rather by a lengthy 
process of sifting through the special requirements of a system specified 
in general terms, often by reference to operational standards in the public 
domain. Numerous case histories point to this lesson. 

In one such case history, the customer — a. major computer manufac- 
turer—knew in broad terms what was wanted (an encoder to convert a 



290 



computer image into a television image), but had practically no idea how 
it should be done. In fact, engineers at this company approached Analog 
Devices because they knew that, somehow, modulation was involved, and 
that we were the undisputed leader in analog multipliers. Ironically, al- 
though these can perform modulation, they would have been a poor 
choice in implementing this function. Thus, we had been the customer's 
first choice on the basis of our known leadership in an irrelevant field! On 
the other hand, many of our other signal-processing skills were very rele- 
vant, and of course, we would say they made a good choice! 

In tte moftths that followed, it took an enormous amount of research to 
find out what rmlly needed to be done. We drew on standard knowledge 
about television, consulted the relevant standards, and talked with special* 
ists in the industry. Bit by bit, pixel by pixel, the design incorporated the 
best of all this knowledge, and has since become a very successful prod- 
uct. But the success of this product cannot, in all honesty, be attributed to 
any fine insights we learned from the one original customer. We got into 
the TV encoder business because, much earlier, we had developed certain 
products (in this case, analog multipliers and mixers) out of an awareness 
of their general utility, and because, once we had sized up the opportunity 
by a few trips down Customer Lane, we then independently researched 
the subject to really internalize the challenge. 

During the early days of Analog Devices this pattern used to be fairly 
common: we'd demonstrate competence in some field, by having made a 
unilateral decision to add a novel function to the catalog (sometimes on 
the whim of a solitary product champion), without a clear voice from the 
marketplace, then later would discover that these generic competencies 
aroused the attention of new customers for ASICs and USICs. The task 
of picking winners was later entmsted to a small committee, which met, 
sporadically and infrequently, in pizza parlors, private homes, and Chi- 
nese restaurants. Our batting average was probably no better than what 
might have been achieved by giving the product champions full rein. Still, 
it worked; the catalog swelled, and the stock climbed. Innovation was 
happening apace. And not just in product design, but in new processes, 
new packaging techniques, new testing methods. 

I strongly believe that seeding the market with well-conceived, an- 
ticipatorv generics, the '70s paradigm,' if you like, remains a very ser- 
viceable strategy for a microelectronics company; such here-and-now 
products will probably be of more value to one's customers than a 
quadrivium of questionnaires and a plethora of promises. On the other 
hand, it would be foolish to overlook the profound importance of devel- 
oping and strengthening one's relationships with key customers; without 
them the most daringly innovative product would be so much artfully 
coordinated sand. 

I'm not advocating a mindless return to the methods that happened to 
work well in an earlier age. It is a matter of emphasis. It's about maintain- 
ing a balanced outlook, about the optimal use of resources and about 
mtanaging risk. Innovation is always risky; but deliberately putting the 



It starts with Tomorrow 

brakes on free-spirited innovation is not without risk either. Which would 
you rather do: (1) Bet on a few people who have proven to be well- 
rounded, resourceful, and intimately familiar with tiie techniques aiKi 
systems used in any market sector; instruct them to spend a lot of time in 
mentoring less-experienced employees and in encouraging them to sift 
through the numercHis items of j^ofessional and trade literature (including 
standards documents) in constantly broadening their own awareness of 
the field; give them all the most powerful CAD tools available, and a lot 
of freedom to be creative . . . or , . . (2) Encourage your designers to be- 
come more effective communicators, to write and later review question- 
naires, carry out statistical analysis on the replies, generate product 
recommendations, and then form teams to act on them to the ItHBf? Both 
classes of activity are important. But if you were forced to choiSie be- 
tween scenario (1) and (2), which do you think would be the more potent 
strategy? 

Case Histories in Communications Products 

Analog Devices' involvement in the radio world took a big step forward 
several years ago (although we didn't realize it at the time) when a 
Japanese customer requested a quotation on a special multi-stage log- 
amp. This request had arisen out of the customer's evaluation of our 
AD640. Here was another product that was not the result of a market 
definition process. When it went into production, not a single customer 
had yet been identified. It was the world's first five-stage log-amp, and the 
only log-amp to use laser trinuning to provide very exact calibration. I 
personally felt it was just a good idea to add log-amps to the growing 
repertoire of wideband nonlinear circuits in the catalog, and to continue 
to pursue such products of general value. 

What this customer wanted seemed preposterous: twice the dynamic 
range of the AD640, single- (rather than dual-) supply operation, at about 
one-tenth the power, having new and very tight phase requirements, and 
various other extra features, all in a much smaller package and (of course) 
at some small fraction of the cost of two AD640s. I vividly recall standing 
by the fax machine just outside Paul Brokaw's office, reading with much 
amusement the request that had minutes before come in from our Tokyo 
office, wondering what kind of fools they must think we were to even 
consider bidding on such a thing. After all, we were a high-class outfit: 
we didn't make jelly beans for the masses. 

But the seed (or was it bean!) was planted, and the technical challenge 
took root. I couldn't put it aside. During a lot of noctumal sims (when cmr 
time sharing VAX-780 was more open-minded) I became excited by the 
possibility of actually meeting both the performance and the cost objec- 
tives. At some point, we decided to ''Just Do It," and eventually, out of that 
customer's one-page request came the nine-stage AD606. 1 dispensed with 
the laser-trinmiing used for the AD640, instead pared the design down to 



292 



accurate essentials, found new ways to extend the dynamic range and 
meet the phase skew requirements, threw out one supply, and whittled 40 
pins down to 16. 

However, even though strongly based on the one customer's request 
(which had been articulated as little more than a general desire to com- 
bine the function of two AD640s in a single low-power, low-co&t chip), 
and even though we were listening hard for every scrap of guidance they 
could provide us, the actual specifications for the AD606 were once again 
very hard to elicit from the systems engineers for whom we were specifi- 
cally designing the part. They, it seemed, knew less than we did about 
what needed to be done. So, where these specifications were missing, we 
interpolated and extrapolated with our best guesses as to what an ideal 
receiver would do in the circumstances, adding one or two innovative 
features that weren't in the original request. 

The subsequent learning process surrounding the AD606 project — 
about the systems in which the part was to be used, as well as the accumu- 
lated know-how of designing, specifying, and testing such parts — became 
a majc^ team effort that substantially furthered our capabilities in RF re- 
ceiver circuits for digital phone systems, and opened doors to new oppor- 
tunities. In developing it, we gained invaluable experience and learned 
much that was later to help us advance the state of the art in multi-stage 
log-amps into newer, even stranger territories. 

Before long, the same customer clamored for more function (the addi- 
tion of a UHF mixer), an even lower supply voltage (2.7V min), even 
lower power (20mW), and, of course, all for the same low price! Now we 
were really listening to the voice of the customer, because, in spite of the 
tight margins, the business opportunity looked like a good one. But that 
C-voice was still weak. We were not really being given a performance 
definition for an ASIC, so much as being asked to add general new capa- 
bilities, while lowering the supply voltage and power. Yet again, we were 
forced to do a lot of independent system research to produce a design, for 
which the number AD607 was assigned. 

As it turned out, this design deviated in important ways from the origi- 
nal expectations*^ of the customer (a mixer plus log-amp) in that it relied 
on an overly innovative approach" in order to address some new dynamic 
range issues and circumvent the technical limitations of the all-NPN 
process we had been using for the AD640 and AD606. It used a very 
fast-acting AGC loop with accurate linear-in-dB gain control to imple- 
ment a log-amp in an unusual manner. This time, the customer didn't 
believe our approach would work, mainly, I believe, because no one had 
ever made log-amps in this way before. 



10 N<H from detailed {^fom^ce requiiements, though, even less a suggested archifectuie. Neither 

of these provided. 
1 1 . 'niiiing is all-important; product concepts can be neither too advanced nor too pedestrian. 



It starts with Tomorrow 



So the *AD607* was put on a back burner, even though the forward- 
looking concept was felt to have general market potential in cellular 
phone systems. After some re-thinking we eventually develcqsed the 
AD608, which was just what the customer wanted, although it required us 
to use XCFB, an advanced, and as yet unproven, IC process.*^ The risks 
were weighed; XFCB won. The AD607 was later redesigned on this 
process for use in GSM digital phone systems, in which it promises to 
provide a highly effective solution. 

It's very important to understand that in this, and many similar case 
histories, the barely audible Voice of the Customer quickly gave way to 
the much louder and more authoritative Voice of the Committee that 
wrote the GSM standards, and to the Voice of the Consultants that we 
hired to help us more rapidly progress into this new field. (You notice 
how they're all VOQs?) Thus, in pursuing an innovative approach to prod- 
uct development, a wide range of voices are often being heeded, including 
those all-important ones that sound from inside, the Voice of Conviction 
and the Voice of Commonsense, 

We need to be careful in connection with the last of these voices, 
though. Comfortable common sense can be the nepenthe that smothers 
innovation. All of us are inclined at times to view things in the same old 
fading light, particularly if the accepted solution seems "only common- 
sensical." (l am bound to think of the lemming-like use of op-amps where 
voltage gain is needed. Op-amps arc far from the best choice in many 
applications. How alluring is their promise of ^infinite gain/ but how far 
from the trath! Still, they remain the commonsense choice for thousands 
of users, and new products are ignored.) 

Often, there are situations where we need to pay close attention not so 
much to what the customer may say to us, but to what is really prob- 
lem that is in need of a solution. Thus, only a few years back, the com- 
monsense way to boil a pan of water was to add heat directly, either by 
dissipating a kilowatt or two in an electric resistor, or by the oxidation of 
some energy-rich material (gas, oil, wood, whatever). Few would have 
been so crazy as to have suggested the use of a peculiar vacuum tube 
called a magnetron. In fact, it's pretty certain that no one actually working 
in the kitchen (the Customer, in this case) would have ever thought about 
the need for a different approach to something as prosaic as heating food. 
Yet, the overnight siKcess of the inexpensive microwave oven is just one 
of innumerable examples of products which owe their genesis to a frwfy 
innovative approach to the marketplace-— one that/ore^ee^ an opportunity 
before it is articulated, or even which sees a way of generating a need 
where there currently isn't one. Out of the introduction of the microwave 
oven came a totally new, co-dependent industry, that of instant meals. 



12. XFCB, for "Extra Fast Complementary Bipolar" a DI process bringing long-antieipated benefits 
to low- voltage, low-power circuitry. See later comments on the genesis of tMs IC process. 



294 



Time and again we find that innovation has meant that someone (often, 
literally one person) saw a bold new way of achieving a commonplace 
task, and had heeded the Voice of Courage and proceeded even without 
the slightest hint from the marketplace of its utility. This relentless and 
self-eclipsing search for *a better way' is the hallmark of the innovative 
engineer Thus it is unavoidably true that the innovator is frequently the 
iconoclast: not content with merely making a useful contribution to ad- 
vance the state of the art, he or she seeks to redefine that art, to restart the 
art all over again from a totally different perspective, often obsoleting last 
year's best ideas in the process. 

Histoiy thret^h Dark GHasses 

Gome with me on a journey into pseudohistory. It is a chilly winter's 
evening in November, 1878. A young man of thirty has recently finished 
reading a book about how to be a successful marketeer It was called 
''YOURS IS THE MARKETr subtitled *'How to Find Out What People 
Really Need and Thereby Become Rich and Famous ^ Although it was 
actually written by an inscrutable Japanese sage in Kyoto, it had recently 
b^ome popular through the best-selling translation and Americaniza- 
tion by a famous Harvard professor with the improbable name of Yucan 
Sellum. This book proclaimed that . . the first step to a successfiil prod- 
uct is thorough market research^' and having taken this very much to 
heart, Tom had set out to systematically poll the residents of Menlo Park, 
New Jersey, to find out what they Really Needed. 

He was getting a little tired, first because he'd walked many miles, 
but also because the responses were all so boringly and predictably simi- 
lar, and he felt he'd amassed plenty enough information to comprise a 
statistically-valid sample set. He decided, though, that he'd complete a 
round- 100 inquiries: "That surely will tell me exactly what People Really 
Need," he thought to himself. (In fact, he was subconsciously recalling 
Prof. Sellum's words: *7r is obvious that the more people to whom you 
talk, the more likely it is that you will find out exactly what the People 
Really Need, By the time you have interviewed one hundred people, it is 
only obvious that the probability is close to 100% that you'll know pre- 
cisely what is marketable y) 

He knocked on the 99th door, and started the algorithm. "Good 
evening, sir, my name's Tom Edison, and I am interested to know what 
you might find inconvenient or inadequate about the present way you 
light your home. Is there perchance some improvement that you'd like to 
see on the market?" "I dunno who you are, young man," growled the 
homeowner, "but yes, I can think of a couple of things. First, if you can 
invent a stronger, brighter gas mantle, people will beat a path to your 
door. Those dumed things are always breaking! And second, if you can 
invent a way that causes leaking gas pipes to be self-healing, you'll 



It Starts with Tomorrow 



quickly find yourself off these streets. You can write that down- Here! 
Take this quarter and buy yourself dinner: you look starved!" 

Tom was a little discouraged. Though he was hungry, he didn't need 
charity. Years ago, as a twenty-three-year-old, back in his Newark days, 
he'd niade $40,000 from the unsolicited invention of the Universal Stock 
Printer for Western Union, and had developed several derivatives of the 
Morse telegraph. He'd also breathed new life into Bell's telephone by the 
invention of the more powerful carbon microphone, and he'd invented 
that phonograph thingy, too. It is said he was writing about 400 patent 
disclosures a year. 

No one had wanted the phonograph, of course, nor the improved tele- 
phone, come to that, but Thomas Alva Edison had a pretty keen eye for 
what innovation was all about, and could readily shrug off the myopic 
naysayers. He used to declare that he was a "commercial inventor" who 
worked for the "silver dollar." What he meant by that was that he con- 
sciously directed his studies to devices that could satisfy real needs and 
thereby come into widespread popular use. But, all that was before his 
conversion by Prof. Sellum; ah, those heady days were iht old way of 
doing things, he now sadly realized. 

As he plodded the streets, he felt just a mite resentful. When it came to 
home lighting, he would have really welcomed an opportunity to promote 
his current ideas. Nevertheless, with the noble Professor's words embla- 
zoned across his forehead, Tom went resolutely up the seven steps to the 
final door, and oscillated the brass knocker. Sharp echoes reso^ided from 
within the chilly and austere interior. 

While waiting, he thought: "Hmmm ... I could fix things so that the 
touch of a little button on this door would melodiously ring a bell in the 
living room, and an annunciator panel would show which door was in- 
volved . . ." He became excited as numerous elaborations of the idea 
coursed through his lively consciousness. Then he quickly corrected him- 
self. "Nah, no one's ever asked for that, so it's probably not a good idea." 

As he was reflecting on the senselessness of even thinking about ignor- 
ing the Harvard Professor's sound advice, and actually inventing and 
marketing something that no one had asked for, the door abruptly swung 
open, and a stem, ruddy-faced matron of ample proportions confronted 
him. "YES!?" she hissed. 

"Good evening, ma'am, my name's Thomas Edison, and I'm interested 
in knowing what you find inconvenient or perhaps inadequate about the 
present way you light your home* Is there some improvement that you'd 
like to see marketed?" "Boy, there's nothing in the slightest wrong with 
the lighting in my home. We use oil lamps, the same as all of us in this 
family do, and have done for generations. Now, if you can find a way to 
make our oil-lamps bum twice as bright and twice as long from one fill- 
ing, r/iat would be something you could sell. But since you can't, be off 
with you, and find something better to do with your life!" TTie sound of 
the heavy black door being slammed in his face convinced him that he'd 
listened to enough voices for one night. 



2% 



When Edison got back to his lab, he sank down into his favorite old 
leather chair, and with a sigh of the sort only a marketeer knows, he ran his 
jfingers rtirough his preniaturely graying hair. All the rest of his guys had 
gone home by this late hour. It was already quite dark. He reached over 
and flipped a switch. Instantly, the desk was flooded with a warm yellow- 
ish light, emanating from a glass bottle connected by a couple of coiled 
wires to a generator spinning*^ somewhere in the basement, whence drifted 
the distinctive whiff of ozone emanating from sparking commutators. 

On the desk were the patent disclosures for his new tungsten lamp, 
alongside hundreds of pages of notes on numerous other kinds of filaments 
with which he had experimented. On top of all these was the good Profes- 
sor's best-selling and popular guide to success, heavily dog-eared and 
yellow-highlighted with Tom's fluorescein-fiUed fountain-pen ("Another 
'bright' idea of mine," he'd quipped). From this senunal work, he had 
leamed about a new way to success: Listen to the Voice of the Customer. 

Reaching into the deep pockets of his trench coat, Edison wearily 
pulled out his spiral-bound reporter's pad, and reviewed the day's 
research. The message was clear. Of the 83 that had actually voiced some 
definite opinion, the customers had noted two key improvements needed 
in their home lighting systems: better gas mantles, and higher-efficiency 
wicks for their oil Imsps. "Too bad nobody ever asked me if I had any 
ideas of my own," he sighed, mefuUy recalling Sellum's strong advice 
that the VOC process must be conducted ''with decorum'' and such a 
way that . . . one only elicits those facts which the customer freely wishes 
to impart to the researcher'' (Chapter 13, Para. 13, page 1313). 

Thomas Alva Edison opened one of his large oak filing cabinets, and 
tossed in all the tungsten-filament papers, heaving another great sigh. 
Maybe someday he'd find a use for all that work. He then took a sharp 
pencil and a clean sheet of paper, and wrote: 

*Trip Report, 18th November, 1878. Spent all day doing a VOC in 
Menlo. Spoke with 100 people re lighting improventents; got good 
info, from 83. . . . Action Item: Write Product Development Proposal 
re Improvements to Gas Mantles and Oil-Lamp Wicks. Do before 
Monday exec, council mtng. Call a KJ to consider weaknesses in 
present methods of mnfng mantles. Memo: be sure Monica obtained 
an adequate supply of Post-It™ pads." 

Innovating in tlie Nineties 

Of course, EcMson didn't work that way or write such rubbish. So far as 
we know, he never pounded the streets looking for ideas; as far as we 
know, he never conducted market surveys; he certainly didn't spend his 



13. However, not humming. Edison was fixated on DC, and jealously blinded to the value of AC 

power. 



It starts with Tomorrow 



time generating product proposals. But he did have a flair for knowing 
what was marketable.^^ We probably can't pursue invention in precisely 
the same free-wheeling fashion that Edison did. In certain important 
ways, our world is different. But the boisterous entrepreneurial spirit 
which he and other long-dead pioneers exhibited can still be a source of 
inspiration to us today. The basic challenge remains essentially the same: 
thoroughly master your technologies; become intimately familiar with the 
needs of the market in the broadest possible terms; respond to these, but 
spend only the minimum necessary time, while pursuing new solutions in 
readiness for that moment when the market opportunities that yoa saw on 
the far horizon come into full view of everybody. 

Still, what is it about our world, and the way we innovate nowadays, 
that has changed so much? Why can 7 we still turn out product ideas as 
profusely as Edison did? Why, when eavesdropping on cocktail-time 
conversations, do we technical people chuckle (or maybe sigh) at hear- 
ing someone use such embarrassingly old-fashioned terms as 'Inventor' 
and 'Genius'? First, we must acknowledge that men like Gauss, Henry, 
Ampere, Weber — and Edison — ^were extraordinarily gifted, possessed 
of relentless energy and self-assurance. They were bom into a time 
when the enormous scope of opportunities for electrical and magnetic de- 
vices had yet to be fully understood and their poteiu^y in evefyday life 
demonstrated. Arguably, it*s easy to be a pioneer when numerous un^ed 
and exciting ideas surround you like so many low-hanging plums. 

But is this the correct explanation of their success? Are we not today 
"bom into" a world where the latent potency of global personal com- 
munication systems, enabled by spacecraft and satellites, by cheap 
multi-million transistor DSPs and high-performing analog ICs, is poised 
to transform our lives far beyond what we witness today? This is a world 
in which sub-micron CMOS, lOOGHz silicon germanium heterojunction 
transistors, optical signal-processing, neural networks, nanomachines, 
MCMs, and MMICs are all waiting to be exploited by the eager inno- 
vator. Is it not true that a modem IC company, with its broad range of 
technologies and wide applicabiUty, can be equally a springboard to 
unimagined new conquests? I very much doubt whether it's much harder 
to be a technical pioneer today than it was at the turn of the century. 

Of course, Edison was not inspired by a mythical Prof. Sellum special- 
izing in cute organizational methods. Rather, he devoured the published 
works of another remarkable innovator, Michael Faraday, himself burning 
with the red-hot zeal of an adventurer and world-class discoverer. Faraday 
worked at the fringe. Indeed, when we study the history of the great in- 
ventors, we find that they were often fired by ideas which, in their day, 



14. Usually, anyway; but in defending his empire of DC generators and distrUjiition systems, he 
even used mendacious disinformation slurs to impede Tesla's promotion of AC as a b^ter choiee 
than his own. 



298 



were right at the ambiguous leading edge— really more like a soft slope — 
of some 'new paradigm.' 

Edison was no different in this respect. Many of the ideas he later 
turned to practical advantage were first conceived, but only tenuously 
exploited, in less market-oriented Europe. He owed a great, although 
rarely noted, debt to a Serbian of unequivocally greater genius, Nikola 
Tesia, who wcwrked for Edison for a while.^^ Incidentally, Tesla points to 
another necessary quality of the innovator: long hours. His were 10:30 
a.m. to 5:00 a.m. the following morning, with a brief break for a ritualis- 
tic dinner, every evening, in the Palm Room of the Waldolf- Astoria hotel. 
The interplay between these two innovators makes a fascinating study. 
Edison was the eternal pragmatist who disliked Tesla for being an egg- 
head; he prided himself on "knowing the things that would not work," 
and approached his work by a tenacious and tedious process of elimina- 
tion. Of this "empirical dragnet," Tesla would later say, amusedly: 

"If Edison had a needle to find in a haystack, he would proceed at 
once with the diligence of the bee to examine straw after straw until 
he found the object of his search. I was a sorry witness of such do- 
ings, knowing that a little theory and calculation would have saved 
him ninety percent of his labor."^^ 

But Tesla was also a touchy and difficult man for others to work with. 
He expected the same long hours from his technicians as he himself put 
into his work. For these men, electrical engineering was a vast, unexplored 
frontier, bristling with opportunities to innovate precisely because there 
was yet essentially no electrical industry. Delivered into this vacuum, 
basic inventions could have a dramatic impact; competition would come 
only much later. 

These circumstances are not unique to any age. It's only the details that 
differ as time passes our way. Sure, there are plenty of light bulbs and 
electric motors already^ and plenty of op-araps and microprocessors. The 
chief question for the contemporary innovator in microelectronics is: 
what are there not plenty of? That was the essence of Edison's quest, and 
he accordingly imiagmed, then innovated, ingenious and eminently prac- 
tical electrical, mechanical, and electromechanical devices, with profit 
unashamedly in mind. 

Through the nervously-flashing retinas of his own eyes, Tesla looked 
out on the same world and had startlingly different visions of ttie future. 



15. Tesia introduced him to the wonders of alternating eument. Edison treated him very badly, even 
cheating him out of $50,000 after he successfully completed a project with which Edison chal- 
lenged him, and didn't think he'd achieve. As noted earlier, Edisoti later launched smear cam- 
paigns when it looked like Tesla's visionary ideas about AC power systems threatened the 
conunercial empire based on DC. 

16, Quoted from Tesla, Man Out of Time, by Margaret Cheney, Barnes & Noble (1993), p 32. 



It Star^ with Tomorrow 



including even radio and radar, VTOL aircraft, robotics, and much else. 
But in some respects his approach was similar: like Edison, he was pos- 
sessed of a lot of personal energy and self-assurance; he knew of his 
unique talents. Above all, he had a strong sense of mission and what some 
might regard as a fanatical single-mindedness (see opening quote). Even 
today, the best innovation, in my view, springs from owning the subject, 
and pursuing an individual pilgrimage, toward destinations which are 
largely of one's own making. We aren't making the best products just 
because some customer suggested them to us, or even assured us of big 
orders, but because we have a passion to bring some art, m which we 
have a large personal investment, to the pinnacle of perfecticm. 

Opportunity, imagination, Ant^pation 

When we look at the world intersected by the time-slice given about 
equally to each one of us, what do we see? Opportunities! Not fewer (be- 
cause "all the good inventions have already been made" and "all the prac- 
tical needs of the market are already being satisfied by a huge industry"), 
but many more, precisely because of the massive infrastructure that now 
exists. 

Think about how hard it would have been in Faraday's time to wind a 
solenoid. Where would he have obtained a few hundred feet of enameled 
copper wire? Not from the local Radio Shack. Undaunted, he imagined 
his way forward. Today, making a solenoid is literally child's play, fedeed, 
many of today's kids are doing things with technology that would baffle 
Faraday. Thus empowered by the infrastructure, our level of innovation 
can be so much more potent; we can do great things with the technical re- 
sources at our disposal. While Faraday may have spent a week or a month 
or a year getting the materials together and then winding a coil or two, we 
just order what we need from the Allied catalog. 

So the 'innovating-in^a-vacuum-was-easy' theory doesn't make a lot 
of sense; it couldn't have been any easier because there was no infra- 
structure: it was probably a lot harder. Today, we are beset on all sides by 
astounding technology waiting to be put to innovative use. And just like 
Faraday, Edison, and Tesla, and all those other pioneers, we need to an- 
ticipate the imminent need for this or that new component — from what 
we know of the market's current needs, and based on what we know 
about our technologies, whether primitive or advanced — and to anticipate 
its value and realize its potential before everybody else does. These as- 
pects of innovation are timeless, and they are not strongly susceptible to 
methodological enhancement by clinical studies of innovation in the 
Harvard Business Review (though they make interesting reading). 

Still, we haven't answered the question about how our world is differ- 
ent from earlier times. Might it be the high complexity and sophistication 
of modem technological projects? Faraday's solenoids, Edison's filament 

300 



lamps, carbon microphones, DC motors and dynamos, and Tesla's 
super-coils and induction motors, though revolutionary, seem in retro- 
spect quite simple, almost naive. Perhaps that's part of it. But underlying 
even the most complex of modem devices, circuits, and systems, there 
are always just a few simple ideas. For example, there is today a strong 
market need for exceptionally-low-noise amplifiers, in medical ultra- 
sound equipment, in analytical instruments, and in many communication 
systems. The principles of low-noise design have not altered for decades; 
this is not at all a matter of complexity, but of sound engineering practice 
based on a clear understanding of cosmic clockwork. Yet here, as in so 
many other situations, opportunities for innovative solutions remain. 

Even complex microprocessors make use of conceptually simple high- 
level logical entities, the details of which become quite secondary in exe- 
cuting a design, which, furthermore, is often only evolutionary, based on 
a large existing knowledge base. Architects of megamillion-transistor 
memories are no more innovative than those advancing the state of the art 
in the underlying cells that are used in such memories. The complexity 
argument seems to be a red herring. 

Maybe today's markets differ in that they are mature: they are already 
well served by many effective solutions, offered by numerous competing 
companies. 

There can be no doubt that it is easier to innovate when there are sim- 
ply no existing solutions, and no one else in the field with whom to com- 
pete. "Edisoii had it easy!" you might say; "Bring him back into these 
times and see just how well his genius would serve him!" I've often won- 
dered about that. The modernist's view of the world, and an awareness of 
the seductive power of myths, leads one to realize that the great figures of 
history were probably not in any essential way much different from you 
or me. The notion that the era of Great Innovation and Pioneering is past 
could be enervating. Certainly, Edison would be a very different figure 
in today's world, but we can only speculate about whether heM achieve 
more, or less. 

I believe we are right at the edge of a massive thrust forward into the age 
of what I like to call '^itronics,' by which I mean electronics in the ser- 
vice of knowledge. Such systems are electronic only because electronics 
provides cheap, miniature, and very fast substrata for the realization of 
knowledge systems, not because of any essentially-electrical aspect of 
the fimction of these systems. The term epitronic points to this 'floating- 
above' aspect of complex data-handling systems: what they are tran- 
scends what they are built from. Today, general-purpose computers are 
the most obvious 'knowledge engines'; their internal representation is 
entirely in the form of dimensionless logical symbols; the fact that their 



it starts with Tomorrow 



processing elements happen to be electrically-responding gates is only 
incidental; computers are in no philosophically important way electronic; 
they belong to the class of epitronic systems. 

Communication channels, by comparison, handle knowledge in transit, 
that is, information. (Knowledge accumulates when information flows; 
thus these are an integral/derivative pair, like voltage and charge.) Com- 
munications systems are physical — they are *more Newtonian' in that 
they are essentially electrical, and involve signal representations that have 
profoundly significant dimensions, such as voltage, current, energy, 
charge, and time, present in components that also have dimenskmal at- 
tributes, such as resistance, capacitance, and inductance, and have junda- 
mentally temperature-dependent behavior. These differences in the way 
we utilize electronics may someday lead to two quite separate fields of 
endeavor. Even now, there are hundreds of computer architects in the 
world who know little or nothing about how circuits work, nor do they 
need to. But the situation is different for the conmiunications system de- 
signer, who invariably does need to be acquainted with both digital and 
analog signal-processing techniques,*^ and very fluent in at least one. 

There are other ways in which our times differ from those of the last 
century. For one, corporations have to be concerned about their obligation 
to the investment community and the appearance of the finaiickls m the 
quarterly report. As a consequence, there is much less room for taking 
risks. Taken to an extreme, the minimization of risk requires a retreat into 
the safe harbor of incrementalism. In the heyday of the late 19tih century, 
this was not such a critical issue governing business decisions. In a mod- 
ern microelectronics culture, we tend to encourage fishing in safe waters, 
rather than undertaking bold journeys out onto the high seas in search of 
uncharted territories and islands of opportunity. 

For another, Edison, and pioneers like him throughout history, were 
rarely seeking just 'better solutions' (such as stronger gas mantles or 
long-life wicks); rather, they were bent on finding radically different ways 
to address widespread unserviced needs. Indeed, the word 'innovate' 
embodies the essential idea of introducing something 'new,' not just *im- 
proved/ Unavoidably, so much of modem microelectronic engineering is 
derivative: the lower-power op-amp; the quad op-amp; the faster-settling 
op-amp ... all doubtless serving real needs, but all based on the same 
traditional approach to feedback amplifier design. 

We need to continually challenge ourselves, by asking such questions 
as: How might this function be approached if the system constraints were 
altered? What lies beyond the op-amp as the next 'universal' amplifier 
cell? How about a microprocessor which is intemally massively-parallel. 



17. It is interesting to note that the scorn poured on 'old-fashionedVaaalog app«©iw?h^ is nowadays 
confined to Che pages of the Wall Street Journal and trade books. Tte job liBlbM fait 
woken up to the fact that experienced analog engineers are in very short suf^ly, which ought to 
have been foreseen. 



302 



and may use millions of transistors, but which has just three pins (VPOS, 
GND, and DATA-CONTROH/0) and sells for a dollar in flip-chip 
form? Ftom what we know about physics, engineering, and the funda- 
mental limitations to realizability, how might 30GHz monolithic trans- 
ceivers be structured and fabricated by the end of the next decade? 

It's unlikely we will be able to fully answer such questions, but it helps 
to think a lot about the far future, which each of us is having a small but 
significant part in creating. In 1945, when the domain of electrical de- 
vices was already quite mature, but electronics was still a brand-new 
word, Arthur C. Clarke, a normally modest Englishman, envisaged a to- 
tally new way of deploying electronic technologies — in a global network 
of satellites in geosynchronous orbits. He even sketched out highly inno- 
vative details of implementation, along with other visionary concepts, in 
his large output of published works.^^ When he n^de these suggestions, 
few would have foreseen the critical importance of communications satel- 
htes in every comer of modem human life. 

There is also the difference of project scale. Today's projects are often 
team efforts, requiring the coordination of many people, often with a sig- 
nificant range of disciplines. But, one may wonder, was it so very differ- 
ent in Edison's time? He was, for example, the Team Leader' behind the 
c<5fl^teiScticm of the generating station on Pearl Stiieet, and for the wiring 
of a few hundred mansions in New York City which this station served. 
One does not need to know all the details to be fairly certain this was an 
interdisciplinary task of considerable magnitude and daring. 

The operative word in this case was not *team' (of course a lot of peo- 
ple were needed to carry out Edison's vision) but 'leader' The image of 
an admired team manager, orchestrating great clusters of dedicated man- 
power, is not supported by the pages of history. He seems to have been 
able to put together groups of technicians whose members worked well 
together, and then set them in motion, but he wanted the public acknowl- 
edgment for the achievement. He is to be credited in the way he antici- 
pated emergent needs, understood the potential of his own ideas, and 
then steered others to actually create the reality, but he was far removed 
from the modem concept of the democratic, team-building engineering 
manager. 

Lei^lffl^hip tn Innovation 

Let's briefly address the tension arising between 'leading' and 'respond- 
ing to' the market, which my Edison parody lamely seeks to illuminate. 
Suppose one reads an ad with the slogan: **National Maxilinear of 
Texas^ — Yoiir Leading Supplier in Microelectronics, Responding to Every 
Need of the Marketplace!" or some such jingle. I don't think that is quite 



it. See, for example, "Extraterrestrial Relays" Wireless W?rW (October 1945). 



It starts with Tomorrow 



a contradiction, but it comes pretty close: to my mind, such a hypothetical 
reference to ^leading' would be weakened by the subsequent reference to 
'responding.' Surely, leadership must involve going ahead of the pack, 
stealthily and methodically seeking new paths, taking the risk that the 
road ahead may be littered with unseen dangers. This doesn't require 
genius. It's leaders, not geniuses, who fight for and claim new t^tories; 
the settlers, with their gilt-framed "Home Sweet Home," rocking chairs, 
and Wedgewood chinaware, come later. 

Edison certainly took risks in connection with his pioneering imm- 
tions, but he did not seem to have regarded hin^lf as a gemus. Nor did 
he need to be, in order to be a strong leader. By contrast, someone such as 
Albert Einstein probably was a, genius, but he didn't possess Edison's 
innovative powers, in the sense that he left no practical invention as a 
legacy, and I think few would describe Einstein as a leader. Edison could 
also conceptualize, but in a nuts-and-bolts sort of way, for he bypassed 
much theory — even scorned it — and set about immediately turning his 
ideas into tangible products for which nobody had yet expressed 
slightest interest, with the full expectation of quickly demonstrating 
ihck practical value. 

History provides abundant lessons of people who forged entire new 
industries out of a singular vision, often one whose potential was totally 
unappreciated by contemporaries. Thus, even though of obvious value 
today, there was no clamor from the public at large for the printing press, 
the telephone, photography, vacuum tubes and the cathode-ray tube, the 
superhet receiver, tape recording, the transistor, the plain-paper copier, 
digital watches, pocket calculators, the Sony "Walkman," the CD player, 
or countless other examples. Each of these were the outcome of a stub- 
bom conviction, often on the part of just one person, that some idea or 
another had intrinsic utility and could generate whole new markets, not 
merely serve the measurable market. 

We noted earlier that Edison's method was "to innovate devices that 
could satisfy real needs and thereby come into widespread poputeuse." 
It was necessarily based on a strong sense of what those needs were — or 
would be! This paradigm, it seems to me, is the essence of leadership, 
which, as an obvious — even tautological — ^matter of definition, means 
leading, not following; anticipating, not merely responding. Two exam- 
ples, gleaned from idle breakfest-time reading, of leadershiprinspired 
innovations for which absolutely no prior market existed, are worth qttot- 
ing here. The first is the invention of the laser, reported in the October 
1993 issue of Physics Today in an article by Nicolaas Bloembergen, who 
first reminds us of the ubiquity of the laser: 



19. Lew Counts drew my attention to an article entitled "The Shock of the Not Quite New" in The 
Economist of June 1 8th, 1 994, in M?hich it is noted that "lawyers at Bell Labs wei?e initially 
unwilling to even apply for a patent of their invention, believing it had no possible relevance to 
the telephone industry." This brief article is well worth reading. It includes several other illus- 
trated examples of innovations which went unrecognized until much later, including the steam 
engine, the telephone, radio, the computer, and the transistor 



3D4 



''The widespread commercial applications of lasers include their 
use in fiber optic communication systems, surgery and medicine, 
printing, bar-code readers, recording and playback of compact 
discs, surveying and alignment instnmients, and many techniques 
for processing materials. Laser processing runs the gamut from 
sculpting corneas by means of excimer laser pulses, to the heat 
treatment, drilling, cutting and welding of heavy metal in the auto- 
motive and shipbuilding industries by COj lasers with continuous- 
wave outputs exceeding lOkW . . . Lasers have revolutionized 
spectroscopy, and they have given birth to the new field of nonlinear 
optics. They are used extensively in many scientific disciplines, 
including chemistry, biology, astrophysics, geophysics and environ- 
mental sciences . . " 

Of course, it would be foolish to suggest that all of these "devices that 
satisfy real needs" were foreseen by the inventors. But, just what did mo- 
tivate them? Bloembergen goes on: 

"[T]he physicists who did the early work were . . . intrigued by 
basic questions of the interaction of molecules and magnetic spins 
with microwave and millimeter-wave radiation. Could atoms or 
molecules be used to generate such f^iation, they asked them- 
selves, and would this lead to better spectroscopic resolution?" 
[Italics mine] 

The motivation in this case seems to have arisen from the desire to find 
a way to greatly improve an existing technique (spectroscopy) and thus 
open up new possibilities (higher resolution). That sounds like incremen- 
talism. On the other hand, although we cannot be sure, it is doubtful that 
the laser was the result of a survey of other physicists as to what they 
perceived would be useful. Rather it appears to have been a spontaneous 
invention by physicists who knew what would be useful to other physicists 
out of their own experience. 

Cannot we do the same sort of thing? Are not we aware of advances 
that, even though not yet expressed by our users, are nevertheless known 
to be valuable? Perhaps the development of new integrated circuits ahead 
of market demand cannot be compared to such a monumental leap for- 
ward as the invention of the laser. Still, there is no reason why the same 
spirit of leadership cannot be present even in this humble endeavor. 
Furthermore, the essential idea of innovating out of a broad knowledge of 
the possibilities and utilities of one *s technologies applies equally in both 
cases. 

My second example is of another *big' idea, the invention of nuclear 
magnetic imaging (NMI), whose full potential is only just beginning to be 
realized: indeed, it is thought by some that NMI will soon surpass X rays 
in medicd diagnosis* NMI came out of nuclear magnetic resonance 
(NMR) techniques which were originally developed to investigate nuclear 



It Starts with Tomorrow 



properties. Jn Science (10 December 1993), George Pake is quoted as 
having this to say about the sources of the ideas: 

"Magnetic resonance imaging could arise only out of the nondi- 
rected research, not focused on ultimate applications, that gave rise 
to what we know today as NMR. TTie key was the series of basic 
quests to understand the magnetic moments of nuclear spins; to 
understand how these nuclear magnets interact in liquids, crystals 
and molecules and to elucidate the structure of molecules of chemi- 
cal interest. Out of these quests cma^ the knowledge that en- 
abled a vision of an imaging technique. Without the basic research, 
magnetic resonance imaging was unimaginable." [Italics mine] 

I'm not suggesting that our primary mission as individual integrated- 
circuit designers, or as team members, or as this or that microelectronics 
corporation, is to conduct basic research. But even in our industry, we 
cannot allow these 'basic quests' to be ignored. This requires that we 
constantly reflect on the utility of new circuit functions, or consider new 
topological reahzations, or pursue advanced silicon processes, or time- 
saving testing techniques, before their need has been articulated by our 
customers, and to relentlessly search for novel ways of ustog c«ir tech- 
nologies to produce "devices that satisfy real needs." Sure, the pressures 
to meet even known market demands are unrelenting, and seem to con- 
sume all available resources. Nonetheless, some of our time mw^f be 
spent in *nondirected research' if we are to continuously strive toward 
leadership. 

ManyVbices 

Nowadays, as already noted, we are more than ever being urged to pay 
close attention to the Voice of the Customer. And, as already noted, there 
are frequently situations in which this makes eminently good sense. 
Faced with the need to respond to an emerging market requirement about 
which we may know little, it is valuable to solicit would-be customers 
about their specific needs. Of course, if we had been practicing good 
gatekeeping skills, accumulating a large body of relevant knowledge 
about our industry, and keeping abreast of new standards by representa- 
tion on relevant committees, the criticality of the customer interview 
would be substantially reduced. Furthermore, we could address our cus- 
tomers as equal partners, with advice to offer proactively, and solutions 
readily at hand. 

By contrast, the textbook VOC technique requires a neutral interview 
procedure, using two representatives, one of whom poses a series of pre- 
viously formulated questions (invariant from customer to customer) while 
the other takes notes as the customer responds. I can think of ao more 
infertile approach to understanding the true needs of the customer, and 



306 



hope thai actual VOC practice differs substantially from this inflexible 
characterization, which would represent the antithesis of leadership. 

Responding to the market makes sense in certain cases. Clearly, it 
would be foolishly presumptuous, and very risky, to imagine that we can 
lead out of our own superior knowledge in every situation. But risks re- 
main, even with the most enlightened and fastidious market research. Oi^ 
obvious danger is that, if we depend excessively on the custcwners' inputs 
to fuel our innovation, we have no advantage over our competitors, who 
can just as easily work through the same VOC procedures and presum- 
ably arrive at an equally potent assessment of a particular opportunity. 
Further, the 'blank page' approach could lead our customers to believe 
that we know little or nothing about their requirements, and that we are 
therefore unlikely to be in any position to offer novel or cost-effective 
sohitions. 

The value of the VOC process is presumed to lie in its efficacy in ex- 
tracting key nuggets of knowledge from the customer. This may be illu- 
soiy;€listoinars may be quite unable to imagine a better way of solving 
their system problems, and may doggedly present what are believed to be 
needs (stronger gas mantles) while failing completely to appreciate that 
there may be several better alternatives. 

Indeed, if the VOC process is cons^ained to a question-and-answer 
format, we may actually be prevented from volunteering our views about 
novel approaches, like Edison with his vision of Electric City, much less 
show how excited we are about these. Sometimes, customers may decide 
to withhold critical information from us, for various reasons. For exam- 
ple, they may have become tired of spending their time with an endless 
stream of VOCers signing in at their lobbies; it may be that the individu- 
als being interviewed had been told by their supervisor not to reveal the 
intimate details of some project; they may have already made up their 
minds that National Maxilinear of Texas, Inc. is going to be the vendor, 
because of all the good ideas they presented, and the leadership image 
they projected, at their last on-site seminar; and so on. 

Thus, the formal VOC process is inevitably of limited value. It is 
merely a way of responding to the marketplace, and as such is bound to 
be lagging the true needs of the market. Though important, it clearly is 
not the primary path of leadership, which requires the constant anticipa- 
tion of future needs. I am not, of course, advocating the abandonment of 
customer interviews, merely noting diat they are only one of numerous 
gatekeeping activities with which all key contributors in an innovation- 
based company — not just those formally designated as 'strategists' — 
must be involved. 

Mtistngs from System Theory 

Since ttds is being written for the enjoyment of those in the microelec- 
tronics community, we might perhaps invoke some familiar ideas from 



It Starts with Tomorrow 



control system theory, and liken the VOC process to a feedback system. 
The basic objective of negative feedback is to minimize the error between 
some desired set point (in this case, the customer's specifications) dxul Ute 
current state of output (the products we have in the catalog). Signals at 
various points along the path (products under development, new concepts 
in our portfolio, and the like), and the nature of the path (business and 
technical procedures) also determine the state of the control system, 
which, to be effective, requires continually sensing the customer's most 
recent needs. 

The output of this system also has some noise (the uncertainty of local, 
national, and global economies, lack of knowledge about competitors' 
product plans, resource collisions, and so on), requiring that decisions 
about optiiiial actions be based on incomplete or corrupted data. In fact, 
this *market-responding' system has a great deal of noise in it, which 
translates to a significant dependence on judgment in dealing with its 
indications. 

Hie seductive promise of a feedback system is that one eventually ends 
up with essentially no error between the 'set point' and the state of the 
system (that is, we meet the customer's clearly articulated needs com- 
pletely). However, as is well known, the inertia inherent in any control 
system, mainly due to the presence of delay elements in the lo^, can lead 
to long settling times or even no stable solution at all Furthermore, feed- 
back systems are less successful in coping with inputs (market demands) 
that are constantly changing, due to this very inertia. Sometimes, when a 
sudden large change is needed, they exhibit slew-rate limitations (tb^ is, 
there's a long ramp-up time to get to the solution, as when a new package 
style may 'suddenly' be needed). 

I'd like to suggest tihat the leadership approach is more like an open- 
loop system. Such systems can be made extremely fast and effective, at 
some expense in final accuracy, which is bounded by the quality of the 
input data (now based on a trust of one's key technologists, and their 
broad, rather than specific, market knowledge) and by the accuracy of the 
implementing system (knowledge about how to optimally achieve the 
final state, that is, practical engineering knowledge). Noise is still there, 
but being based on long-term data (fundamental physical lis&ations of 
devices and technologies, durable principles of design, long familiarity 
with a wide variety of customer needs, well-established standards which 
will impact a large number of customers to result in similar demands, and 
so on) the noise is heavily filtered before it enters the system. 

Thus, with a stronger emphasis on leadership, the reliance on a low- 
bandwidth, possibly oscillatory closed-loop system must be replaced by a 
dependence on a fast, direct response based on a comprehensive, 
sure-footed knowledge of the market in rather general terms, and the 
technologies and the design skills which can quickly be deployed in an 
anticipatory manner. 

Open-loop (predictive, feedforward) systems are well kiiovm for their 
inherent stability and for being able to track rapidly changing inputs; in 



our analogy, this means that we are ready with that special package 
before the product is nearing release — ^because its need was anticipated, 
knowing of the current trends in manufacturing techniques among one's 
customers — and that one is ready with the next product at about the same 
time that the latest part is being released. 

Incidentally, this raises an interesting strategic challenge: How soon 
should a company introduce foUow-up products, in an *open-loop' fash- 
ion (before the demand is obvious) so as to stay on the competitive curve, 
knowing that these will inevitably cause some erosion in the sales of ear- 
lier products? Historically, many IC companies haven't been particularly 
adept in addressing this question. Clear opportunities for follow-up action 
are often neglected, because of the concern that some product "released 
only last quarter" might be obsoleted too soon. To be competitive, one 
doesn*t have much choice: leadership requires making those decisions 
without waiting for the clamor from the customer. They should be based 
on a sound understanding of trends and in anticipation of market needs, 
rather than waiting for that coveted million-piece order to be delivered to 
the doorstep. 

But this is not really an either-or situation. One needs a judicious 
balance of both approaches (leading and following, anticipating and re- 
sponding) to be completely effective. However, current philosophies and 
policies in the microelectronics industry, designed to improve the success 
rate of new products and minimize investment risk, point away from the 
traditional emphasis on leadership-based innovation and the freedoms 
granted the product champion that proved so successful in earlier times. 
Are the practices of those times still relevant? That's not clear. 
Nevertheless, it seems to me that it is preferable to do business based on 
long-term internal strengths than to depend too much on going "out 
there" to get the critical information needed to make reliable business 
decisions. 

Leadership is required to be successful in all product categories. For 
standard products, the challenge is to constantly be on the watch for com- 
petitive threats, and have an arsenal of next-generation solutions always 
on hand. These products need a high level of predictive innovation, moti- 
vated by a keen awareness of what the customer will probably need two 
to five year^ from now, as well as what emerging technologies will be- 
come available in one's own factory, in competitors' factories, and in 
advanced research houses. This requires judgment about trends, and a 
good sense of future product value and utility. In the control theory anal- 
ogy, the development of standard products is likely to benefit from the 
'feedforward' approach. It will be the Voices-of-Many-Customers that are 
here important, as well as the Voices-of-Many-Competitors, as indirectly 
articulated in their ads, their data sheets, and their application notes. 

Special-purpose ICs, on the other hand, are clearly more likely to ben- 
efit by listening to the Voice of sometimes just One Key Customer, maybe 
two or three, as well as the Voices of Committees (writing standards, 



It starts with Tomorrow 



recommending certain practices), and the Voices of Consultants (people 
hired to advise a company about some new and unfamiliar field or spe- 
cialized domain of application) aini finally^ because of the pcrtsably low 
margins of most high- volume products (almost by definition), one needs 
to listen to the Voice of Caution. The challenge here is first, to grasp some 
less familiar new function, or set of functions, or a whole new system; 
second, to achieve a higher level of system integration (manage complex- 
ity); third, to achieve a very low solution cost (since one is competing 
with existing well-known costs and/or other bidders); fourth, to get to 
product release fast on a very visible schedule; fifth, to ramp up quickly 
to volumes of many thousands of parts per month. In the development of 
special-purpose ICs, the customer is, of course, the primary reference, the 
* set-point' in the innovation feedback system. 

Innovation and TQM 

Product quality has always been important, but it is especially critical in 
modem microelectronics, as competitive pressures mount andmarket 
expectations for commercial'grade parts now often exceed those required 
only by the severest military and space appUcations a few years ago^ but 
at far lower cost. During the past few years, the airport bookstores have 
been flooded with overnight best sellers crowing about the im|)ortance of 
'excellence' in modem corpoi^ions, and how to foster a cultiire in which 
excellence is second nature. Sounds like a good idea. But excellence 
alone is not enough to ensure success: 

"Excellence . . . will give [companies] a competitive edge only until 
the end of the decade. After that, it becomes a necessary price of 
entry. If you do not have the components of excellence . . . then you 
don't even get to play the game." 

says Joel Arthur Barker.^ Quality for quality's sake doesn't make much 
sense. It wouldn't help to have perfect pellicles, 100% yields, zero deliv- 
ered ppm's and infinite MTBFs unless the products that these glowing 
attributes apply to have relevance in the marketplace, and are introduced 
in a timely fashion. They are, to paraphrase Barker's comment, "merely 
essential" requirements of the business. 

Hie need for a strong focus on quality is self-evident, widely appreci- 
ated, and has received a great deal of attention in recent times. This em- 
phasis, commonly referred to as Total Quality Management, or TQM, is 



20. Joel Arthur Barker, Paradigms: The Business of Discovering the Future (1994). It appears that 
this book was previously published in 1992 under the title fu/iire Edge. I gu^s by te time 
anything with the word "Future'' in its title was becoming pass6 — so perhaps it ^j^^ only 
lackluster sales; by contrast, "Paradigms" became a very marketable word in 1994. 



310 



clearly essential and must be relentlessly pursued. One of the many 
sub-goals of TQM (all of which have 3LAs and 4LAs that are very effec- 
tive in numbing the mind to the importance of their underlying concepts) 
is Design for Manufacturability, or DFM. 

However, some seasoned designers do not respond favorably to the 
formalism of TQM. This is probably because they feel slightly insulted 
that anybody would assume they were prone to overlook the obvious 
importance of such things as DFM. They are also bemused by the appar- 
ent 'discovery of quality' as a new idea. They may feel that the notion that 
one can legislate quality by the institution of formal procedures, such as 
checklists of potential mistakes and omissions, is somewhat naive. Many 
of the rituals, observed with near-religious fervor, and recommended 
practices seem overly regimented. Thus we read, in a much respected 
manual of instruction^* 

**3. Ten to twelve feet is the distance at meetings and seminars. In a 
meeting or seminar situation, try having the speaker first stand about 
1 5 feet from listeners and then stand 30 feet from listeners. Moving 
farther away from listeners noticeably changes the speaker's rela- 
tionship to the audience. During a meeting the instructor should be 
about 10 to 1 2 feet from most of the participants. After the formal 
session, the instructor can move to the 4 foot distance for an infor- 
mal discussion and refreshments." 

Are you listening, Mr. Edison? If your ghost is ever invited to make an 
after-dinner presentation at a modem company, you'd better get that little 
matter straight. It's this sort of 'institutionalizing the obvious,' and the 
evangelical emphasis of method over content, of process over product, 
that many of us find irritating and counterproductive in contemporary 
TQM methodologies. 

There's also the old-fashioned matter of pride of workmanship at 
stake. Skilled designers believe they have an innate sense of what is man- 
ufacturable and what is not, and they exercise constant vigilance over the 
whole process of finding an optimal solution with manufacturability very 
much in mind. For such persons, it is quite futile to attempt to mechanize 
the design process, if this means applying a succession of bounds on what 
methods can and cannot be used. Strong innovative concepts and products 
cannot thrive in a limiting atmosphere. 

Design quality is never the result of completing checklists. It is even 
conceivable that by instituting a strong formal mechanism for checking 
the design one could impair this sense of vigilance, replacing it with the 
absurd expectation that mistakes will assuredly be trapped by checking 



21, Shoji Shiba, Alan Graham, and David Walden, A New American rfiA/ (Productivity Press, 
19«K 298. 



It ^rts with Tomorrow 



procedures. Nor does quality increase when the number of signatures 
increases. There is no disagreement with the idea that design checking is 
important. It can catch errors which might easily be overlocted and allow 
designers to benefit from hard-won experience. But this function needs to 
be integrated into one's workplace, and be active, in a background mode, 
continuously throughout the development. 

In the long mn, this quality-enhancing process will benefit by being 
automated, using our workstations and company-specific 'experience 
databases.' For now, this will be limited to what can be done with present- 
day computers. It will depend on giving all who need it essenti^y itist^t 
access to massive amounts of knowledge about our business; it will de- 
pend on building more helpful monitoring agents into our tools, that catch 
anomalies; it will often depend on providing quite simple pieces of code 
to reduce a keyboard-intensive task to a single keystroke; it will depend 
on the pioneering use of teleconnections of all sorts to link together geo- 
graphically disparate groups. 

In a future world, the quiet time that our machines have when (iO we 
go home at night will be used to review our day's work: in the morning, 
there'll be a private report of our oversights, indiscretions, and omissions, 
for our personal benefit. To err is humiliating, and particularly so in pub- 
lic; but to have one's errors pointed out in private can be enriching* I Sin- 
cerely believe that such aid will eventually be available, but of course it is 
far from practicable today. Nevertheless, there are many 'intelligent' ways 
in which automated assistance can be built into design tools, such as cir- 
cuit simulators. Some are very simple 'warning lights' that would advise 
of improper operating conditions in a circuit; others will require substan- 
tial advances in artificial intelligence before they can be realized, such as 
agents that can detect the possibility of a latch-up, or a high-current fault 
state, in some topology. 

Is Design a Science or an Art? 

Should one emphasize the science of design over the art of design, or vice 
versa? This is of considerable interest in academia, where the challenge is 
not usually to pursue excellence by participating in the actual design of 
innovative, market-ready products, but rather, by choosing the best para- 
digm to instill in the minds of students who wish to become good design- 
ers in industry. 

The distinction between science and art is quite simple. Science is con- 
cerned with observing 'somebody else's black box' and about drawing 
conclusions as to how this black box (for example, the physical universe) 
works, in all of its various inner compartments. Science is based on exper- 
iment, observation, and analysis, from which basic material scientists then 
suggest hypotheses about the underlying laws which might plausibly lead 
to the observed behavior. These hunches cmi be tested out, by droiq)ing 
sacks of stones and feathers off the Tower of Pisa, or by hurling unsus- 



312 



pecting protons around electromagnetic race tracks. The experimental 
results acquired in this way require further analysis. If all goes well, the 
huHifeie hy{)€She$is gets promoted to the status of Theory. 

While hypothesis-generation and the creation of grand theories can be 
said lo be a constructive, even artful, endeavor, it often amounts to little 
more thm trying to find ways to figure qut how 'somebody else's pieces' 
iit tcgether. Science is (or should be) primarily a /lario/i^^t^^^a^ 
ity. In electronics, we might speak of reverse engineering (referring to the 
process of finding out how your competitor was able to achieve perfor- 
mance that you thought was impossible, by tracing out the schematic of 
his circuit) as a 'science.' However classified, though, practice repre- 
sents the antithesis of innovation, by general agreement. 

Art, on the other hand, is about seeing the world in an ever-fresh way. 
The artist often scorns previous conventions as worthless anaphronisms. 
The challenge to the artistic temperament is to create a new reality, even 
while building on old foundations. Thus, the painter sees the blank canvas 
as an opportiaiity to portray his or her personal vision of our world (or 
some other non-world); the composer sees the keyboard beckoning to be 
set afire wift an exciting new musical statement. Certainly, there is practi- 
cal skill needed in handling art ntedia (a knowledge of how to mix paints, 
forexan^le, or of the principles of harmony and counterpoint), but the 
artist's primary locus is di creative, striving, synthetic activity. In the 
artist's life pulses the ever-present belief that the old conventions can be 
pushM far beycttid^eir known limits, or even be overthrown completely. 
Analysis of the kind pursued by technologists is foreign to the mind of 
the artist. 

The painstZLking process of innovating sophisticated, competitive IC 
products embraces a considerable amount of *art.' This is not a popular 
idea, for it evokes such images as *ego-trip,' 'open-loop behavior,' 'loose 
cannon,' ^disregard for conununity norms,' 'abandoning of sound prac- 
tice,' and other Bad Things. Which is a pity, because designing an inte- 
grated circuit is very much like painting in miniature, or writing a piano 
sonata: it's the creation of a novel entity, the distillation of our best efforts 
into something small in scale but big in importance; it is craftsmanship at 
the limits of perfection, and at its best, transcending these limits into new 
realms of expression. When this impulse is faithfully acted upon, quality 
of design will be essentially automatic. The science has been sublimated; 
it*s still there, like the knowledge of paints or harmony, but it permeates 
the whole creative process without needing to be raised to the top levels 
of consciousness.^^ 

True, engineers are not explicitly paid to be artists, and admittedly 
we'd be in deep trouble if we designed our ICs just so that the layout 



22. We can be thankful that Rembrandt and Beethoven or Shakespeare did not have to sign off 
quality checklists before their works could be relied to the world. 



It Starte with Tomorrow 



looked pretty. But that is not at all what I have in mind. Perhaps a better 
word, for now, niight be * artfulness,' that is, an approach to design which 
cannot readily be captured in a formal set of procedures. An aMil design 
is one that calls on a wide range of deeply felt ideas about the intrinsic 
correctness of certain techniques, deviating from the ordinary just far 
enough to open new doors, to push the envelope gently but firmly toward 
ever more refined solutions, in lively anticipation of tomorrow's demands. 
This view about the relevance of art in design is shared by Joel Arthur 
Barker, who writes^^ 

"Some anticipation can be scientific, but the most important aspect 
of anticipation is artistic. And, just like the artist, practice and per- 
sistence will dramatically improve your abilities. Your improved 
ability will, in turn, increase your ability in dealing with the new 
worlds coming." [Italics mine] 

Perhaps one can criticize this 'artistic' view of the design challenge as 
having an appeal only to a certain kind of mind, although it seems that a 
love of engineering and a love of the visual and musical arts often go 
hand in hand. I happen to believe it is central to the quality theme, and 
that it is overlooked because we work in a business — indeed, live in an 
age — ^^where it is presumed that everything can be measured, codified, and 
reduced to a simple algorithm, and that profound insights can be mapped 
on to a three-inch-square Post-It™ and comfortably organized within an 
hour or so into a coherent conclusion and set of action items. This is a 
deeply misinformed philosophy; it's part of the 'instant' culture that sadly 
we have become. 

Certainly, there are times when team members need to get together 
and look for the *most important themes,' to help us simplify, as much 
as possible, the various challenges that beset us. The problem, it seems to 
me, is that the process takes over; the need to use the ^correct method,' 
under the guidance of a 'facilitator,' who alone knows the right color of 
marker pen to use, gets slightly ludicrous. But who dares speak out in 
such a sacred circle? I personally believe that corporations which put a 
high value on such rituals will one day look back and wonder how they 
could have been so silly, though I realize this is not a politically correct 
thing to say. 

With all of the 'quality improvement methods' now being pursued like 
so many quests for the Holy Grail, there is little likelihood that the sci- 
ence will be overlooked; it is far more likely that we will dangerously 
underestimate the value of the art of design. Those various 'quality algo- 
rithms' should be regarded as only guidelines. They cover some rather 
obvious principles that always need to be observed. But they also over- 
look some very subtle, equally crucial, issues, which are often specific to 



23. Ibid. 



314 



a particular product or design activity, and are usually extremely difficult 
to articulate in algorithmic form. The innovation of competitive high- 
quality microelectronic components is both a science and an art. Neither 
is more important than the other. 

Innovation in microelectronics is not, of course, limited to product 
design. There is need for innovative new approaches across a broad front, 
particularly in the development of new IC fabrication processes, involving 
many team members. At Analog Devices, the utilization of bonded wafers 
as a means to manufacture a dielectrically isolated substrate is a good 
example from recent history. This was a step taken independently by the 
process development team, and had no VOC basis, though the technology 
it now supports certainly had. They even had to make their own bonded 
wafers in the early days, and I'm sure it was out of a conviction that here 
was a brand-new approach that promised to allow a step-function advance 
to be made in IC technology. 

The eventual result of this anticipatory research was an outstanding 
technology (XFCB) which unquestionably enjoys a world-class leader- 
ship position. It includes an innovative capacitor technology and retains 
the thin-film resistors that have been a distinctly innovative aspect of 
Analog's approach to IC fabrication for more than twenty years. The 
perfection of these ultra-thin resistors was another hard- won battle, un- 
dertaken because of the dogged conviction on the part of a handfiil of 
believers that the benefits were well worth fighting for. 

Sometimes, innovation involves the bringing together of many loosely- 
related processes into a more potent whole, such as the laser-trimming of 
thin-film resistors at the wafer level.^ This required an innovative syn- 
ergy, combining significantly different design approaches, altered layout 
techniques (the use of carefully worked-out resistor geometries), and 
novel test methods (involving the use of clever on-line measurenient tech- 
niques to decide what to trim, and by how much). 

At each of these levels, there was also the need for independent inno- 
vation: thus, the precise formulation of variants of the resistor composi- 
tion needed to achieve a very low temperature-coefficient of resistance 
(TCR); the control of the laser power to minimize post-drift alteration of 
this TCR, and thus maintain very accurate matching of trimmed networks 
over temperature; understanding the importance of oxide-thickness con- 
trol to prevent phase-cancellation of the laser energy; development of new 
mathematical methods to explore potential distributions in arbitrarily- 
bounded regions; the realization of the potency of synchronous demodu- 
lation as a better way to trim analog multipliers; and so on. These, and 
many other advances by numerous contributors, were needed to bring the 
science of laser-wafer trimming to a high art. 



24. Dm Sheingold reminded me of this, in reviewing a draft of this manuscript, and suggested LWT 
as an example of what might be called collaborative innovation. 



It starts virith Tomorrow 



Knowtedge^^iven liinovat^^ 

I would like to suggest some ways in which we might raise the rate and 
quality of innovative output in a real- world IC development context. 
Obviously, good management and mentoring on the part of skilled seniors 
is important, but to a significant extent, the management of innovation is 
largely about the management of knowledge. And electronics, as already 
noted, has become an indispensable servant of knowledge. Colin Cherry 
writes^ 

"Man's development amd the growth of civilizations have depended, 
in the main, on progress in a few activities — the discovery of fire, 
domestication of animals, the division of labor; but above all, in the 
evolution of means to communicate, and to record, his knowledge, 
and especially in the development of phonetic writing." 

Just as the invention of writing radically altered all facets of human 
endeavor, today's computers can help us in numerous knowledge-related 
contexts to achieve things which only a few years ago were quite impossi- 
ble. This is hardly news. The question for us here is, how can we make 
more effective use of computers to put knowledge at the disposal of the 
innovator? 

We noted that the creative spark may well be a random event, mere 
cranial noise, but it is only when this is coupled into a strong body of 
experience and encouraged by a lively interest in anticipating — and actu- 
ally realizing— the next step, that we have the essential toolkit of innova^ 
tion. Unfortunately, many of us are quite forgetful, and even with the best 
record-keeping habits cannot quickly recall all that we may have earlier 
learned about some matter. 

It is often said that today's computers still have a long way to go be- 
fore they can match the human mind. That's obviously true in some im- 
portant respects; lacking afferent appendages, it's hardly surprising that 
they are not very streetwise. And they have been designed by their master 
architects to be downright deterministic. But they are possessed of prodi- 
gious, and infinitely accurate, memories, unlike our own, which are in- 
variably fuzzy, and depend a great deal on reconstructive fill-in. They are 
also very quick, giving us back what is in RAM within tens of nanosec- 
onds, and knowledge fragments from several gigabytes of disc within 
milliseconds. Obviously, in accuracy of memory recall, and possibly even 
in actual memory size, computers really have become superior, and I 
don't think there's much point in trying to deny that particular advantage. 

Computers are also very good at relieving us of the burden of compu- 
tation. There is no virtue in working out tables of logarithms {as Charles 



25. CoJin Cherry, On Human Communication (New York: Wiley, 1957), 31. 



3t6 



Babbage noted, and decided to do something about, with the invention 
of the ^difference engine*^^) and there is no virtue in using those tables, 
either; we can, and should, leave such trivia to our silicon companions. 
Not oiily are they flawless in calculation, they are very, very quick. These 
calculations often go far beyond pri 

SPIG3E, for example, we are invoking naaay, many man-years of experi- 
ence with the behavior of semiconductor devices. Who reading this has 
niemorized all of the equations describing current transport in a bipolar 
transistor, or would wish to manually develop the numbers for insertion 
into these equations? Here agiun, I do not think it silly to assert that com- 
puters are far better than we. Sure, they aren't painting stilMifes like Van 
Gogh, or writing tender sonnets, but they can run circles around all of us 
when it comes to sums. Round two to computers. 

They have another advantage over us. They will work night and day 
on our behalf, and never complain nor tire. While we sleep, the net- 
works chat; updates of the latest software revisions mid databases si- 
lently flow and are put into all the right places, ready for us to do our 
part the next day. We surely need to be honest in acknowledging that 
in this way, too, they definitely have the edge; we have to black out for 
a considerable fraction of each and every day. We need to take full ad- 
vantage of these valuable knowledge-retaining, knowledge-distributing, 
and knowledge-based-calculating attributes of our indefatigable silicon 
companions. 

Modem innovators have a critical dependence on operational knowl- 
edge across a broad front. This includes knowledge of the microelectron- 
ics business in general terms, knowledge of one's specific customers 
(who they are, where they are, and what they need), knowledge of one's 
IC process technologies, of semiconductor device fundamentals, of circuit 
and system principles, of one's overall manufacturing capabilities and 
hmitations, and on and on. It is widely stated these days that knowledge 
is a modem company's most valuable asset. That much ought to be obvi- 
ous. But while a lot has already been done to automate manufacturing 
processes using large databases, progress in making design knowledge 
widely available to engineering groups has been relatively slow in becom- 
ing an everyday reality. 

Most IC designers will readily be able to recall numerous instances of 
having to spend hours chasing some trivial piece of information: What is 
the field-oxide thickness on the process being used for a certain product? 
What is the standard deviation of certain resistor widths? Where is there a 
comprehensive list of all intemal memos on band-gap references? Where 
is there a scale-drawing of a certain IC lead-frame? Each of these could 
be reduced to a few keystrokes, given the right tools. Instead, the quest 



26. See, for example, Babbage's memoirs Passages from the Life of a Philosopher published by 
Rjjtgers University Press, with an introduction by Martin Campbell- Kelly (1994) for the back- 
ground to the invention of the "difference engine." 



It starts with Tomorrow 



for these rudimentary fragments of essential knowledge can (and often 
does) erode a large fraction of each day. 

At Analog Devices, we have developed a datatese prograan which 
represents an excellent start toward providing answers to these sorts of 
questions. In the long run, our effectiveness in reducing development 
time, in lowering costs, in enhancing quality and much else, is going to 
increasingly depend on much more massive and interactive databases — 
better viewed, perhaps, as knowledge networks. While primarily having 
a technology emphasis, such networks would allow querying in a wide 
variety of ways, about the business in general, and they would dim be 
deeply integrated into our development tools. 

They would be available at all levels and throughout the entire develop- 
ment cycle, starting with access to relevant public standards, the market 
research process, product definition phase and prior art searches, through 
actual component design and checking, layout and verification, wafer fab, 
early evaluation, test development, packaging, data sheet preparation, 
applications support, and beyond, to customer fe^l^ck, and so cm. These 
electronic repositories would provide information on many other vita! 
matters, such as resource scheduling, all in one place, available for search- 
ing, browsing, consulting, and interacting with, anywhere, anytime, as 
instantly as keystrokes. 

The data itself would be in many forms (text, hypertext, graphics, 
schematics, drawings, schedules, sound bites, and, asmultimedia capabil- 
ities expand, video clips). It would represent the ainassed e^qp^riM of 
hundreds of contributors. The operational shell should support much 
more than a mere searching function — it would be interactive and antici- 
patory, pointing to other sources of relevant or coupled information; that 
is, it will work with relational databases. It should be possible for any- 
body with the necessary level of authority to make additions to the data- 
bases, and it should allow masking of the field of inquiry; that is, the 
interaction process would also be amenable to personalization. 

Because of their immense commercial value, many parts of such data- 
bases would require protection of access. Many individua;ls would be 
given access to only certain databases; as a general rule, the new hire 
would be given minimum access to critical information, while sMior em- 
ployees would have access to a very wide range of knowledge about the 
whole business. The whole question of security is fraught with contradic- 
tions and dilemmas: knowledge which is so potent that one's conmercial 
success depends on it would obviously be very dangerous in the wrong 
hands. However, that cannot be raised as a fundamental reason for not 
providing access to 'world-class' knowledge. In all likelihood, developers 
of such databases will need themselves to exhibit considerabfe innovation 
in developing ways to temper this two-edged sword. But I cannot imagine 
how one can be competitive in the long mn without serious attention to 
such a knowledge network. 

It would take much imaginative planning and immense effort to turn 
this Promethean undertaking, easily stated here, into reality. Clearly, this 



318 



is about the development of a resource that is much more than a way of 
finding valuable bits of information without significant delay. I see it as 
being the basis for propagating ideas throughout a corporation, as a men- 
toring vehicle, as a way to keep track of one*s project schedules (and 
ensure that all their interdependencies are properly calculated) and much 
else. I would expect it to take advantage of the most recent developments 
in dxe management of large depositories of knowledge, and to make use 
of the latest multimedia hardware. 

This is something that decidedly cannot be achieved by one or two new 
hires with degrees in computer science, or even a highly motivated and 
well-qualified software innovator. It will require the full-time efforts of a 
large team, headed up by a respected leader in this field reporting into a 
high level of the company. Is it too far-fetched to look forward to the time 
when COmpBBt^ have a VP of Knowledge? This person would not neces- 
sarily come from the world of engineering or computer science. Because 
the objectives set before this person would be so broad and so important, 
they could not be left to generalisms and rhetoric; they would need very 
careful articulation as precise deliverables. 

More than any other initiative, I see this as being one that is most likely 
to bring about real change and be most effective in coping with the vicis- 
situdes of the modem microelectronics world. And I would go so far as to 
assert that is it precisely because the task is so monumentally difficult that 
one may be inclined to tinker with the latest management methodology 
instead, in the hope (funny, I first typed that as h-y-p-e) that there's still 
another one or two percentage points yet to be squeezed out of the guys 
and gals on the production floor through the implementation of another 
new procedure with another mystical name. Perhaps I just don't get it. 

itthancing Innovation 

Is there anything else that can be done to encourage, elevate and propa- 
gate the innovative spirit? How might our high-quality innovative output 
be enhanced? I think there are many ways. First, a little early success as 
we start out on our career can make a big difference. I recall how valuable 
it was to me to be heartily praised for my mmor (and often deviant!) ac- 
complishments as a new boy at Tektronix. It immensely strengthened my 
resolve to do something the next day that was truly deserving of praise! 
And it was so different from the bureaucratic, authoritarian, rule-based 
structure which Fd worked under as a junior in England. 

Those of us with managerial and mentoring responsibilities need to do 
all we can to help new hires to see tangible proof of their value to the com- 
pany, as quickly as practicable. From the very start, we need to provide 
and sustain an elevated sense of the possible. This tmst-based cultivation 
of a sense of worth, character, responsibility, and potency is of prime im- 
portance, not only in raising expectations, but in actually fiilfiUing them. 
Analog Devices has traditionally succeeded very weU in this respect. 



It starts wttti Tomorrow 



Second, for all of us charged with innovation, getting out into the field 
and talking one-on-one with customers, not just as voices on the phone, 
but as people in their own working environment, is crucidly important. 
Our customers are not always right, but when they are we can't afford to 
miss their message. However, it will by now be abundantly clear that I 
believe this is too narrow a description of the challenge, a view that is 
shared by many of my fellow technologists. In addition to listening to our 
customers, we need to pay attention to numerous other voices, including 
the all-important internal Voice of Conviction about which projects make 
sense and which are likely to be dead ends. 

The provision of a supportive corporate infrastrucmre is also of im- 
mense value; if we feel we are trusted to make good decisions, empow- 
ered to achieve great results, and then provided with powerful tools^ we 
almost certainly will succeed. A palpable interest from the top is of ines- 
timable value. Working at Tektronix in the mid-sixties, I was impressed 
by the fact that its then-president, Howard VoUum, and many of the VPs, 
would frequently tour the engineering areas, usually dressed down in 
jesms and sneakers, and talk with us designers about our latest ideas at 
some length. They would push buttons, twiddle knobs, and administer 
words of praise, advice, and encouragement. That kind of interest, visibil- 
ity, and personal involvement on the part of senior managers is often lack- 
ing in modem corporations, much to their loss. 

The element of risk is an essential ingredient of innovation. Once we 
allow ourselves to bdieve that ttere are textbook ways of achieving grea^ 
ness, we are doomed; Strong-mindedness, conviction, and comfmtoent 
can compensate for a lot of missing data and counterbalance a certain 
amount of misjudgment, an idea echoed by these words by Analog 
Device's Ray Stata: 

"In the case of Nova Devices [now ADI] there couldn't be a better 
example of the necessity of a lot of will power and commitment 
because it was a very, very rocky experience. In these companies 
which are basically high risk in nature, you really have to have 
somebody who decides on a course of action — don't know 
whether fanatical is the word — ^but with tremendous conviction in 

terms of what they want to do and why it's necessary to be done 

All the reasons why it cannot be done are somehow submerged, 
even those with validity. There has to be a capacity to take great 
risks and not all that much concern about the fact that you might 
not make it." 

— (From an interview conducted by Goodloe Suttler, 
at the Amos T\ick School of Business, 1980) 



320 



Coniptiters: or ^ffipantons? 



I have already exposed my views about the superiority of computers in 
certain activities, but have a couple of other things to add about the er- 
gonomics of innovation. The designer's most important tool is the 
high-speed workstation. Time-to-market considerations, increased circuit 
complexity, accuracy of simulation, and design for manufacturability 
demami that our machines be state-of-tte-art. A study of work habits 
would almost certainly reveal that a circuit designer^'' is seriously 
bounded by machine speed, and spends a large part of the day simply 
waiting for results. 

This seems like a confession of poor work habits. It may be asked: 
Why don't you do something else during that time? The answer is simple. 
First, many simulations are of fairly small cells undergoing intensive 
optimization: tiiere is a lot going on in one*s mind as each simulation is 
launched; small changes are being explored, the consequences compared; 
and while that is happening, the next experiment is already being assem- 
bled in the shunting yard of the mind. The process is a fluttering dynamic, 
demanding instant resolution. We want to be at all times mind-limited, 
not machine-limited. 

Typically, what happens is this. A simulation is launched, and the re- 
sult is expected to be available in perhaps ten seconds, perhaps twenty 
seconds, perhaps half a minute. None of these intervals is long enough to 
start another project of any magnitude. So instead of being completely 
idle, we may on occasion find ourselves pecking away at some text file in 
Mother window on our CRT. But the design process requires strong focus 
and full concentration to achieve our rapidly developing objectives. It is 
difficult to deflect one's attention from a flood of conscious thought about 
these goals toward some secondary cerebral occupation. These machine 
delays evoke a frustration not unlike trying to enjoy an exciting adventure 
movie on a VCR with the pause button depressed for much of the time by 
a mischievous prankster. 

We have a long way to go before we can be completely happy with the 
performance of workstations in a circuit development context. We have 
seen significant improvements in such things as memory space: the most 
adviaiced workstations (such as those from Silicon Graphics Inc.) provide 
up to 512 megabytes of RAM, and several gigabytes of hard disk. Now- 
adays, raising CPU speed, and the use of superscalar instruction cycles 
and multiple parallel processors, represent the new frontier. Hopefully, 



2'7. Other computer users, such as layout designers and test engineers, also need fast machines, but it 
is the computationally intensive aspect of circuit simulation that most seriously (telays circuit 
development. 



It S^trts with Tomorrow 



IC designers will only be limited by what the computer suppliers can 
provide, and never by poor judgment on the part of managers as to how 
much one can "afford" to spend on fast machines. 

We might reflect that our competitors are faced with exactly the same 
limitations as we (unless their computer budget is significantly larger) and 
thus the challenge facing each of us is to find ways of improving our effi- 
cient use of the machines we already have. Part of the solution may be in 
revising our work habits, although the problems of machine-gated cre- 
ativity, just described, are real. Another piece of the solution, though, is 
to continue to emphasize the value of proprietary software. 

When one considers the critical role played by computers and software 
in today's competitive arenas, and the importance of operational knowl- 
edge, there can be little doubt that the most important way in which man- 
agement can help to advance one's innovative potency is through the 
establishment of a much larger CAD activity. I do not think this is the 
time to be winding down or holding steady, relying exclusively on 
third-party vendors of 'turn-key' (ha!) software. IC companies need to 
be especially careful about harboring the naive belief that large softw^e 
houses are exclusively capable of providing the tools needed for making 
the future. One may on occasion choose to buy some standalone software, 
but it is axiomatic that, being forced to use generally the same software as 
everyone else, and to an increasing extent, obliged to use the same tech- 
nologies as everyone else (such as foundry-based sub-micron CMOS) 
one's competitive advantage will be limited to what can be achieved with 
marketing prowess and design skills alone. 

Thus, in my view, the future success of any company that aspires to a 
high rate of innovation will significantly depend on a very strong in-house 
CAD activity. A major and urgent objective of that CAD Group wouM be 
the implementation of an interactive knowledge network embodying mas- 
sive amounts of essential information, organized in such a way as to be not 
only readily accessible, but also in some way to offer help proactively. It 
will be the incredible potential of networked computers to tirelessly inform 
and illuminate our lives as engineers, as well as their continued use as cal- 
culating tools, that will bring about the largest improvements in innovative 
productivity. A more effective union of thinking machines and cerebrally- 
sparkling human minds promises to radically alter everything we do. 

But we should not imagine that the demands on human energy and the 
need for creative thrust and sparkle will be lessened. Norbert Wiener, in 
God and Golem Inc., has this to say: 

"The future offers very little hope for those who expect that our 
new mechanical slaves will offer us a world in which we may rest 
from thinking. Help us they may, but at the cost of supreme demand 
upon our honesty and intelligence. The world of the future will be 
an ever more demanding struggle against the limitations of our in- 
telligence, not a comfortable hammock in which we can lie down to 
be waited upon by our robot slaves," 



322 



Nevertheless, the computers we will be using as we pass through the 
portals into the coming millennium, some 5,000 years since the invention 
of writing, will, I am convinced, be more like silicon companions than 
mere tools, even less like "robot slaves." Before that can happen, we will 
need to radically revise our ideas about what our machines ought to be 
allowed to do, and ideas about how much free will we wish to impart to 
them. This is destii^d to be an area of tremendous innovation in its ovm 
right. Computer experts may disagree. Many seem to wish machines to be 
forever deterministic. They would argue that if, for example, one enters a 
command with a slightly deviant syntax, or points to a non-existent direc- 
tory, or allow a spelling error to creep into a file name, it is not up to the 
machine to look for a plausible meaning and offer it back to the human 
for consideration. That might lead to anarchy. 

I strongly disagree with that view. Please! — Let the computer make 
these suggestions, and help me, its fumbling, memory-lapsing human 
user. Many of these 'little things' can be, and are, easily performed on 
present-day machines. Thus, the UNIX command set filec will usefully 
exp^md a truncated file name into its completed form.^^ But on other occa- 
sions, even using the most recent workstations, we get very nearly the 
same old dull reactions to our aberrant requests as we did back in the old 
DOS days. A handful of heuristics is invariably helpful That's often the 
human's most important way forward; why shouldn't machines be given 
the same advantage? 

Soii^ believe that there is little point in attempting to make machines 
"like us." Erich Harth writes^^ 

It is still intriguing to ask the question *What if?' W/z^r// our en- 
gineers succeed in constructing a truly thinking computer? And 
what if. to complete the illusion, we could clothe it in an audio- 
animatronic body, making a perfect android, a human recreated in 
silicon hyperreality? Would it have been worth the effort? Certainly 
there is value in the exercise, the challenge to our ingenuity. But the 
final product would be as useless as Vaucanson's duck. The ultimate 
kitsch! There are easier ways of making people, and anyway, there 
are too many of us already.*' 

The image of *'a perfect android" is not what I have in mind; such an 
entity might istked be of as much value as a distinctly dull-minded junior 
assistant. This description completely fails to take into account what a 
"silicon hyper reality" might do. Freed of our own frail forgetfulness, and 
our emotional variability, endowed with a bevy of Bessel functions in the 



28. If one believes that creativity is merely what happens "when normally disparate frames of refer- 
ence suddenly merge," as Koestler believes, then eould one say that in some tiny way the raa- 
ciuie is dtHng a creative act in makbig this decision on our behalf? 

29. Erich Haith, The Creative Loop: How the Brain Makes a Mind (Reading, MA: Addison- Wesley 
Publishing Company, 1993), 171-172. 



It Starte with Tomorrow 



bowels and Fourier integrals at the fingertips, knowledgeable of all of the 
best of Widlar's and Brokaw's circuit tricks, our imperfect, but highly 
specialized, android, The KnowledgeMaster Mk. /, could be a tren^mlous 
asset. He need not move; but remote sight would be useful (in scanning 
those old papers of Widlar that we leave on the desk), and hearing may be 
essential, not only in freeing up our fingers, but in eavesdropping on the 
engineering community (a la HAL, in 2001: A Space Odyssey, which, 
incidentally, was another vision from the neurally noisy mind of Arthur 
C. Clarke), 

A brief consideration of earlier projections of what computers might 
"one day" do leads us to be struck by how limited these visions often 
were. We've all heard about the early IBM assessment of the U.S. market 
for computers being about seven machines. Isaac Asimov, another noted 
visionary, imagined a time when robots might check our texts \mt dkin^t 
seem to anticipate how utterly commonplace and powerful the modem 
word processor, and in particular, the ubiquitous spelling-checker, would 
become. In his science-fiction story^^ Galley Slave he portrays an android 
named Easy who specialized in this task, and has the storyteller marvel at 
how 

"With a slow and steady manipulation of metal fingers^ Easy turned 
page after page of the book, glancing at the left page, then the right 
. . . and so on for minute after minute . . . The robot said, 'TMs is a 
most accurate book, and there is little to which I can point. On line 
22 of page 27, the word "positive" is spelled p-o-i-s-t-i-v-e. The 
comma in line 6 of page 32 is superfluous, whereas one should have 
been used on line 13 of page 54. 

I wonder how many young users of the program I'm using to write this 
essay— Microsoft™ Word — know that, less than forty years ago, its capabil- 
ities were solely the province of sci-fi? Probably very few people living 
back then would have believed that robots who could correct our spelling 
and even our grammar would become commonplace so soon. A page or 
two later in Asimov's story we hear the robot's promoter say, over objec- 
tions about allowing such powerful machines to enter into our daily affairs: 

"The uses would be infinite, Professor. Robotic labor has so far 
been used only to relieve physical drudgery [in the futuristic setting 
of this story-BG]. Isn* t there such a thing as mental drudgery? 
[You'd better believe it-BG]. When a professor capable of the most 
creative thought is forced to spend two weeks painfully checking 
the spelling of lines of print and I offer you a machine that can do it 
in thirty minutes, is that picayune?" 



324 



30. Ga/ory (December 1957). 



Thirty minutes! We are already irritated if it takes more than a few 
seconds to perform a no-errors spelling check on something of about 
the length of this essay. Users of Microsoft™ Word 6.0 can now have 
spelling errors trapped on the fly, with their author's most probable inten- 
tions proffered for consideration (another one of those examples of an 
emergent capability for Koestler's creative conjugations of frames of 
reference, perhaps?). Modem word processors can also do a tolerably 
good job of correcting bad grammar Note in passing how much we de- 
pend on being able to personalize the dictionaries and rules behind these 
checkers; my little PowerBook 180^ on whom I daily cast various spells, 
has already become a serviceable, though still rather dull, companion. 

Are we being equally shortsighted in seeing how tomorrow's connec- 
tion machines will be capable of serving our needs as innovators? In 
visualizing the mmy further ways they could perform more than mere 
'spelling checks' on circuit schematics (that is, going beyond catching 
just gross errors — ^roughly equivalent to grammar checking)? Even with- 
out an independent spirit, there is much they could, and I think, will help 
us with. Eventually freed from the frustrations of not being able to find 
the information we need to do our job, aided by more liberally minded 
machines, and allowed to operate in a strongly anticipatory mode, design- 
ers in all fields could make great strides toward more rapid, more accu- 
rate, ^md more effective development of new products. Our visionary use 
of the leverage afforded by prodigious auxiliary minds could make an 
inmense difference. 

Ultimately, we may even decide that it's not so stupid to build into 
these machines, very cautiously at first, some sections which are 
* afflicted' by noise. We will have to get used to the idea that these bits 
may not behave in the same way every day, that they may even cause our 
silicon companion to have moods. It is this propensity for unpredictability 
and irrationality that makes people interesting. Like latter-day Edisons, 
we are, insofar as machine intelligence is concerned, just on the threshold 
of a whole new world of opportunity, a future (not so far off, either) 
where we will, for the first time in human history, need to be sensitive to 
the emerging question of machine rights. . . . There are no ready-made 
solutions, ripe for exploitation, in this domain; we will need to decide 
what kind of assistance we, as innovators, want our knowledge-gatherers 
and collators to give us, and just how much of the excitement of engineer- 
ing we w^t to share with them. 

A better vision of this future is found in a new book^^ by David 
Gelemter, who writes 

"But why would anyone want to build a realistic fake mind? Is 

this really a good idea? Or is it pointless — or even dangerous? 

"That's an important question, but in one sense also irrelevant. 

The urge to build fake minds stands at the nexus of two of the most 

31 . David Gelemter, The Muse in The Machine: Computerizing the Poetry of Human Thought (New 
York: The Free Press, 1994), 48. 



ft wth Tomorrow 



powerful tendencies in the histories of civilization. These two are so 
powerful that it's pointless even to contemplate notpmmmg thxs 
kind of research. It will be pursued, to the end. 

''People have always had the urge to build machines. And 
people have always had the urge to create people, by any means 

at their disposal— for example, by art The drive to make a 

machine-person is . . . the grand culminating tour deforce of the 
history of technology and the history of art, simultaneously. Will 
we attempt this feat? It is predestined that we will." [original italics] 

What we do with these fake minds is up to us (at least, that's what we 
think today . . .). In less dramatic ways, we already see it happening, and 
there is no doubt in my own watery mind that since machines came on the 
scene, I've been a much more effective innovator. No single microelec- 
tronics corporation can undertake vast journeys of exploration and dis- 
covery into the world of artificial intelligence. For now, we just have to 
recognize that we can become more effective only by putting design and 
marketing knowledge into the hands and minds of every person in our 
design teams. 

Our innovating descendants will probably still be teaching the value 
of VOC techniques well into the next century. But to them, this dusty 
acronym will have long ago become a reference to the wisdom of lis- 
tening to the Voice of the Computer (the old-fashioned name we would 
use today), or rather, reflecting the diminution of its erstwhile merely- 
calculating function, and the by-then commonplace acceptance of the 
total symbiosis with, and essential dependence on, these sentient adjuncts 
to human minds. The Voice of the Companion, Long live VOC! 



Carl Nelson 



19. The Art and Science of 
Linear IC Design 



I have been asked several times by other integrated circuit (IC) design 
engineers, "How do you come up with ideas?" And my answer was usu- 
ally something flip, like "Beats me, it just happens." Later, I began to 
think more seriously about the actual process that I went through to come 
up with new ideas for designs. My motive for figuring out the process was 
mostly curiosity, but I also wanted to document from new design ideas 
and the satisfaction of seeing successful products going out the door. 

What I decided after a little pondering was that good IC design depends 
on a healthy disrespect for what has been, and lots of curiosity for what 
might be. By this I mean that one must assume that we have seen only a 
tiny part of the secrets in silicon, and therefore there are endless discov- 
eries to be made. We must keep ourselves from thinking in terms of per- 
ceived limitations, and instead strike off on new paths, even if they don't 
seem to be going anywhere. On the other hand, engineering is based on 
fundamental laws that stubbornly refuse to let bad designs work well. I 
am continually amazed by engineers who hang on to a concept even when 
it clearly requires the laws of physics to bend. The human brain has a 
wonderful ability to combine what is into what might be, and a good en- 
gineer must let this process charge along, then apply reality checks so 
that mistakes, dead ends, and dumb ideas get cast aside. 

When I tested this philosophy on other engineers, it soon occurred to 
me that from their viewpoint it seemed more like rhetoric than revelation. 
What was needed was details — the engineer's stock in trade. To that end I 
tried to create a list of specific techniques that can be used in analog IC 
circuit design. This probably leaves me wide open to the criticism of ego- 
tism, but it's been my observation that many of the best engineers have 
monstrous egos, so possibly it somehow aids in the design process. I hope 
the following ideas are helpful. If they're not, at least I finally made Jim 
Williams happy by coming through on my promise to do a chapter for 
this book. 

The first section is on inspiration, so it is kind of vague and slippery, 
much like the process itself. The next section is more down to earth, and 
obviously exposes a litany of mistakes I made along the way. We learn 
and remember from our own mistakes, so maybe force feeding them isn't 
too helpful, but that's the way it came out. Good luck. 



327 



The Art and Science of Linear IC Design 



Inspiration: Where Does It Come From? 
Free Ftoating Mind 

Many of the best IC designers agree that some of their great design ideas 
occur outside of the workplace. I Icnow it is true for me, and in my case it 
is usually someplace like the car, shower, or bed. These are places where 
only minimal demands are being made on your mind, and interruptions 
are few, unless you get lucky. (I commute on autopilot. I think there is a 
special part of the brain allocated just for getting back and forth to work. 
It can accomplish that task with only 1 28 bits of memory.) You can let 
your mind float free and attack problems with no particular haste or pro- 
cedure, because you own the time. It doesn't matter that ninety-nine times 
out of one hundred nothing comes of it. The key is to have fun and let 
your mind hop around the problem, rather than boie into it. Don't think 
about details. Concentrate on broader aspects like assumptions, limita- 
lions, and combinations. Really good ideas often just pop into your head. 
They can't do that if you're in the iruddle of some rigorous analysis. 

Trials at Random 

Colleagues think I'm really weird for this one, but it does work some- 
times when you have spare time and pencil and paper. I connect things 
up at random and then study them to see what it might possibly be good 
for. It's mostly garbage, but every so often something good shows up. I 
discovered an infinite gain stage, a method for picoamp biasing of bipo- 
lar transistors, and several new switching regulator topologies this way. 
Unlike the free floating mind mentioned earlier, here you concentrate 
totally on the details of what you've done to see if there's anything useful 
in it. 

One good thing about this simple-minded technique is that it teaches 
you to analyze circuits very quickly. Speed is essential to maximize your 
chance of finding something useful. The other good thing about it is that 
when you do come up with something useful, or at least interesting, you 
can drive people crazy with the explanation of how you thought of it. 

Backifvg In from the End 

A natural tendency for design engineers is to start at the beginning of a 
design and proceed linearly through the circuit until they generate the 
desired output. There are some situations where this procedure just 
doesn't work well. It can work where there are many possible ways of 
accomplishing the desired goal. It's kind of like a maze where there are 
many eventual exits. You can just plow into the maze, iterate around for 
a while, and voil^, there you are at one of the exits. 

There are other situations where this beginning-to-end technique 
doesn't work because the required result can only be obtained in one of 
a few possible ways. Iteration leads you down so many wrong paths that 
nothing gets accomplished. In these cases, you have to back into the 
design from the end. 



328 



The "end" is not necessarily the desired circuit output. It is the restric- 
tions that have been placed on the design. If the circuit must have some 
particiflar characteristic, whether it be at the input, in the guts, or at the 
output, sketch down the particular device connections which must be used 
to accomplish the individual goals. Don't worry if the resulting connec- 
tions are "bad" design practice. The idea here is that there is only one or 
at mo^ a few ways that you can get to where you need to be. After you 
have all the pieces that solve particular parts of the problem, see if it is 
possible to hook them together in any rational fashion. If not, alter pieces 
one at a tinae and try again. This is a parallel design approach instead of 
the more conventional serial method. It can generate some really weird 
circuits, but if they work, you're a hero. 

Testh^f Conventional Wtedom 

Bob Widlar taught me to consistently and thoroughly mistmst anything 
I hadn't proved through personal experience. Bob wasn't always right 
about things, but partly by refusing to believe that anyone else knew 
much about anything, he made great advances in the state of the art. 
Conventional wisdom in the late '60s said you couldn't make a high cur- 
rent monolithic regulator. The power transistor on the same die with all 
the control circuitry would ruin performance because of thermal interac- 
tions. He did it anyway, and the three terminal regulator was bom. The 
funny part of this story is that Widlar said at about the same time that no 
IC op amp would ever be built with a useftil gain greater than 50,000 
because of thermal interaction limitations. Not long after that, op amps 
appeared with gains greater than 500,000. Some designer obviously 
didn't believe Bob's rhetoric, but believed in his philosophy. 

Conventional wisdom is somettiing that constantly intrudes on our 
ability to make advances. Engineers are always using "mles of thumb"* 
and too often we confuse useful guidelines with absolute tmth. By con- 
stantly questioning conventional wisdom I irritate the hell out of people, 
but sometimes it pays off when a new product is bom that otherwise 
wouldn't have happened. This doesn't mean that you should bash around 
trying to get away with designs that are nearly impossible to produce with 
good yield. It means that you should ask people to detail and support the 
limitations they place on you, and then do your damnedest to find a hole 
in their argument. Try to remember your childhood years, when the most- 
used expression was "But why not?" Remain intellectually honest and 
main^n good humor while doing this and you should escape with your 
life and some great new products. 



1. In the sot so dist^t past/men were allowed to use a stick no larger in diameter than Uieir thumb 
to be^ their wives. This useM gtudeline fell out of general use when the Suprerrie Court de- 
cided that wives could not use anything larger than a .38 to defend themselves. 



The Art and Science of Linear IC Design 



Find Solutions by Stating the Problem in Its Irreducible Terms 

This technique has been helpful on several occasions. The idea is to clar- 
ify the possible solutions to a problem by stating the problem in its most 
basic terms. The LM35 centigrade temperature sensor, developed while 
I was at National Semiconductor, came about in this way. At that time, 
monolithic sensors were based on designs that required level shifting to 
read directly in degrees centigrade. I wanted to create a monolithic sensor 
that would read directly in centigrade. More importantly, it needed to be 
calibrated for both zero and span at the wafer level with only a single 
room temperature test. This flew in the face of conventional wisdom, 
which held that zero and span accuracy could only be obtained with a 
two-temperature measurement. 

I found the solution by expressing the desired output in its simplest 
terms. A PTAT (Proportional to Absolute Temperature) sensor generates 
an inherently accurate span but requires an offset. A bandgap reference 
generates a precise zero TC offset when it is trinmied to its bandgap volt- 
age, which is the sum of a PTAT voltage and a diode voltage. A centi- 
grade sensor therefore is the difference between a first PTAT voltage and 
a reference consisting of a second PTAT voltage added to a diode voltage. 
Subtracting two PTAT voltages is simply equal to creating a smaller 
PTAT voltage in the first place. Also, it was obvious that creating a centi- 
grade signal by using span-accurate PTAT combined with zero TC band- 
gap would create a sensor which still had accurate span. By thinking of 
the problem in these terms, it suddenly occurred to me that a centigrade 
thermometer might share symmetry with a bandgap reference. Instead of 
the sum of two opposite-slope terms giving zero TC at a magic (bandgap) 
voltage, it might be that the difference of two opposite-slope terms would 
generate a fixed slope, dependent only on the difference voltage. This 
means that a simple calibration of difference voltage at any temperature 
automatically defines slope. Sure enough, the same equations that predict 
bandgap references show this to be true. The LM35 is based on this prin- 
ciple, and produces very high accuracy with a simple wafer level trim of 
offset. 



Philosophjcal Stuff 

Things Th^ Are1<£)o Good to Be True 

Many times I have been involved in a situation where things seemed bet- 
ter than they ought to be. Eventually a higher truth was revealed, and 
along with the embarrassment, there was much scrambling to limit the 
damage. This taught me to question all great unexpected results, some- 
times to the point where my colleagues hesitate to reveal good fortune if 
I am in earshot. The point here is that the human ego will always try to 
smother nagging little inconsistencies if a wonderful result is at stake. 
This has shown up in recent high-profile scandals involving such diverse 
fields as medicine, physics, ^d even mathematics. 



330 



When the situation arises, I try to make a judgment about the worst 
case downside of embracing results that seem just a little too good. If the 
potential downside is sufficiently bad, I refuse to believe in good fortune 
until every last little inconsistency has been resolved. Unfortunately, this 
sometimes requires me to say to other engineers, "I don't believe what 
you're telling me," and they are seldom happy with my *'too good to be 
true*' explanation. 

A good example of the danger in embracing wonderful results appeared 
in a recent series of editorials by Robert Pease in Electronic Design. He 
took on the hallowed work of Taguchi, who sedcs to Utnk production vari- 
ations by utilizing Statistical Process Control. Taguchi believes that most 
production variation problems can be solved by doing sensitivity analysis 
and then arranging things so that the sensitivities are minimized. He used 
an exan^te in his book of a voltage regulator whose output was somewhat 
sensitive to certain resistors and the current gain of transistors. After some 
fiddling with the design, Taguchi was able to show that it was no longer 
sensitive to these things, and therefore was a '*robust" design. Unfortu- 
nately, Mr. Taguchi didn't bother to check his amazmg results. Pease 
showed that the output was insensitive simply because the circuit no 
longer worked at all ! 

If this was just an academic discussiOT, then one could indulge in what- 
ever level of delusion one liked, but the IC design business is extremely 
competitive, both professionally and economically. A small mistake can 
cost millions of dollars in sales, not to mention your job. I remember an 
incident many years ago when a new micropower op amp was introduced 
which had unbelievably low supply current. I questioned how the current 
could be so low, especially since the start-up resistor alone should have 
drawn nearly that much current. I studied die schematic, and sure enough, 
there was no start-up resistor! The circuit needed only a tiny trickle of 
current to start because it had closed loop current source biasing that 
needed no adcUtional current after starting. This tiny current was appar- 
ently supplied by stray junction capacitance and the slew rate of the sup- 
plies during turn on. This seemed too good to be true and the data sheet 
made no mention of starting, so we purchased some of the amplifiers and 
gave them the acid test; slow ramping input supplies at the lowest rated 
junction temperature. Sure enough, the amplifiers failed to start. I heard 
later that irate customers were returning production units and demanding 
to know why there was "no output." It takes only a few of these incidents 
to give a company a bad reputation. 

Unfortunately, some engineers become so fearful of making a mistake 
that they waste large amounts of time checking and cross-checking details 
that would have little or no impact on the overall performance of a circuit. 
The key here is to emulate the poker player who knows when to hold 'em 
and when to fold 'em. Ask yourself what the result would be if the sus- 
pect result turned out to be bogus. If the answer is "no big deal," then 
move on to other, more important things. If the answer is "bad news," 
then dig in until all things are explained or time runs out. And don't be 



The Art and Science of Linear IC Design 



shy about discussing the discrepancy with other engineers. As a class, 
they love a good technical mystery, and will respect you for recognizing 
the inconsistency. 

Checking Nature's Limits 

Many of the important advances in linear ICs came about because some- 
one decided to explore just exactly what nature's limits are. These ideas 
were developed because someone asked himself, "How well could this 
function be done without violating the basic physical limits of silicon?" 
Studying the limits themselves often suggests ways of designing a circuit 
whose performance approaches those theoretical limite. Hiete's^ old 
saying that is true for linear IC design — once you know something can be 
done, it somehow becomes a lot easier to actually do it. Until you know 
the real limits of what can be done, you can also make the error of teHmg 
your boss that something is impossible. Then you see your competition 
come out with it soon after. A classic example of this is the electrostatic 
discharge (ESD) protection structures used to harden IC pins against ESD 
damage. A few years ago no one thought that you could provide on-chip 
protection much above 2,000V, but no one really knew what the limits 
were. Our competition suddenly came out with 5,000V protection, but got 
smug. We scrambled to catch up and discovered a way to get 15,000V 
protection. We still don't know what the limits are, but we're sure link- 
ing about it a lot more than we used to. 

When I worked in the Advanced Linear group at National Senaicon- 
ductor, we had a philosophy about new design ideas; if it wasn't a hell of 
a lot better than what was already out there, find something better to do. 
This encouraged us to think in terms of the natural limits of things. It 
wasn't always clear that the world wanted or needed something that was 
much better than was already available, but it turned out that in most 
cases if we built it, they bought it. It is my observation that customers buy 
circuits that far exceed their actual needs because then they don't have to 
waste time calculating the exact error caused by the part. They can as- 
sume that it is, at least for their purposes, a perfect component. Customers 
will pay to eliminate worry simply because there are so many things to 
worry about in today's complex products. 

What to Do When Nothing Malces Any Sense 

Everyone has been in group situations where no one can agree on the 
truth of the matter under discussion. This often happens because no test 
exists which can prove things one way or another. In some cases when I 
suggest a test that might prove who's right and who's not, the response is 
total apathy. Evidently, human nature sometimes loves a good argument 
more than truth, and I suppose that if life, liberty, and cable TV are not 
at stake, one can let these arguments go on forever. Engineering is not 
nearly so forgiving. We find ourselves in situations where the cause of 
some undesirable phenomenon must be discovered and ccaracted^ — 
quickly. The problem gets complicated when nothing makes any sense. 



332 



An engineer's nightmare consists of data that proves that none of the pos- 
sible causes of the problem could actually be the real cause. My favorite 
phrase after an engineer tells me that all possibilities have been exhausted 
is "Hey, that's great, you just proved we don't have a problem!" 

Of course life is not that simple, and the challenge is to identify a new 
series of tests which will clearly show what is going on. The great thing 
^out Ais mj»tal process is that it soix^times leads to a solution even 
before the tests are run. Defining the tests forces you to break down the 
problem into pieces and look at each piece more carefully. This can reveal 
subtleties previously hidden and suggest immediate solutions. 

The first step is to challenge all the assumptions. Ask all of the people 
involved to state their assumptions in detail and then make it a game to 
blow a hole in them, A good engineer is more interested in solving prob- 
lems than protecting ego, so give and take should be welcomed. 

The classic mistake in problem solving is mixing up cause and effect. I 
have been in many meetings where half the crowd thought some phenom- 
enon was a cause and the other hMf considered it an effect, but no one 
actually expressed things in these terms, so there was much pointless 
arguing and wasted time. 

Order of the testing is critical when time is short. Tests with the highest 
probability of success should get priority, but you should also consider 
the worst-case scenario and start lengthy tests early even if they are long 
shots. Nothing is more career-threatening than explaining to your boss 
well down the road that your pet picks came up empty, and that you will 
now have to start long term tests. 

The final step is to pre-assign all possible outcomes to each of the 
tests. This sometimes reveals that the test won't prove a damn thing, or 
that additional tests will be needed to clarify the results. My rough esti- 
mate is that 30-40% of all tests done to locate production problems are 
worthless, and this could have been determined ahead of time. If we were 
in the pencil making business, it wouldn't be a big deal, but the IC busi- 
ness runs in the fast lane on a tight schedule. I have seen fab lines throw 
mountains of silicon at a bad yield problem simply because they have no 
choice — ^the customer must get silicon. All lines have problems, but what 
separates the winners from the losers is how fast those problems get fixed. 

There are certain kinds of problems with circuits that defy all attempts at 
clever or sophisticated analysis. Cause and effiect are all jumbled, complex 
interactions are not understood, and no tests come to mind that would 
isolate the problem. These electronic Gordian knots must be attacked not 
with a sword, but with the san^ technique used to untangle a jumbled 
mess of string. Find an end, and follow it inch by inch, cleaning up as you 
go until all the string is in a neat little ball. I find that very few people 
have the patience or concentration to untangle string, but for some reason, 
I get a kick out of it. The electronic equivalent consists of taking each part 
of the circuit and forcing it to work correctly by adding bypass capacitors, 



The Art and Science of Linear IC Design 



forcing node voltages or branch currents, overriding functions, etc. When 
you have the circuit hogtied to the point where it is finally operating in 
some sane fashion, it is usually much easier to isolate cause and elfect. 
Then you can start removing the Band- Aids one at a time. If removing 
one causes the circuit to go crazy again, replace it and try another. Try to 
remove as many of the unnecessary Band-Aids as possible, checking each 
one to make sure you understand v^hy it is not needed. Hopefully, you will 
be left with only a few fixes and they will paint a clear picture of what is 
wrong. If not, take your children fishing and practice on backlashes. 

Don't Do Circuits That Try to Be Everything to Everybody 

I have seen many linear IC products introduced which are touted as a 
universal solution to customer needs. These products have so many 
hooks, bells, and whistles that it takes a 20-page data sheet just to define 
the part. The products often fail in the marketplace because: (1) They are 
not cost effective unless most of their features are used. (2) Engineers 
hate to waste circuitry. (3) Customer needs ch£mge so rapidly that com- 
plex products become obsolete quickly. (4) Engineers subconsciously 
tend to allow a certain amount of time for learning about a new product. 
If they perceive that it will take much longer than this to be able to design 
with a new circuit, they may never get around to trying it. 

The most successful linear IC products are those which do a job sim- 
ply and well. The products themselves may be internally complex, such 
as an RMS converter, but externally they are simple to use and under- 
stand. Flexibility should not be provided to the user by adding on a pile 
of seldom-used optional features. Instead, the chips should be designed to 
operate well over a wide range of temperature, supply voltage, fault con- 
ditions, etc. A well-written data sheet with numerous suggesticMis for 
adapting the chip to specific applications will allow users to see the use- 
fulness of the part and to make their own modifications that give them 
ownership in the final application. 

Use Pieces More Than Once 

For reasons I have never figured out, I love to make pieces of a circuit 
do more than one function. And like love, this can be both d^mgerous 
and exciting. Actually, before ICs it was standard procedure to make 
tubes or transistors do multiple duty, either because they were expen- 
sive, or because of space limitations. Engineers became heroes by sav- 
ing one transistor in high- volume consumer products . Nine^transistor 
radios performed nearly as well as modem IC designs that use hundreds 
of transistors. Transistors on a monolithic chip are literally a penny a 
dozen, and they are tossed into designs by the handful. Even discrete 
transistors are so cheap and small that they are considered essentially 
free. 

So why should designers discipline themselves in the archaic art of 
not wasting transistors? The answer is that like ^y other skill, it t^es 
practice to get good at it, and there are still plenty of situations where 



334 



minimalist design comes in very handy. One example is when a change 
must be made to an existing design to add an additional function or per- 
formance improvement, or to fix a design flaw. To avoid expensive re- 
layout of a large portion of the IC, it may be necessary to use only the 
components already in the design. A practicing minimalist can stare at 
the components in the immediate area, figure out how to eliminate some 
of them, and then utilize the leftovers to solve the original problem. He's 
a hero, just like in the old days. 

Micropower designs are another example where double duty comes in 
handy. Every microampere of supply current must do as much work as 
possible, A transistor whose collector current biases one part of the circuit 
can often use its emitter current to bias another part. The bias current for 
one stage of an amplifier can sometimes be used for a second stage by 
casGoding the stages. There are certain classes of Imndgap reference de- 
sign where the reference can also do double duty as an error amplifier. 
These and many other examples allow the designer to beat the competi- 
tion by getting higher performance at lower current levels. 

Often, I don't see many of the minimizing possibilities until a circuit is 
well along in design, but that is the best time to look for them. All the 
pieces are in front of you and it is much easier to see that two pieces can 
be morphed^ into one. If you do this too early, you tend to waste time 
bogged down in details. At the very end of the design such changes are 
risky because you might forget or neglect to repeat some earlier analysis 
that would find a flaw in the design change. Keep in mind also that future 
flexibility in the design may be compromised if too much fat is removed 
originally. 

I Ntfim* Met a Burn-ki Circuit I Ulced 

One of my pet peeves concerns testing rehability with bum-in. This is 
standard procedure for all IC designs and the typical regimen during 
product development is a 125°C bum-in on 150 pieces for 1000 hours at 
maximum supply voltage. Bum-in is supposed to detect whether or not 
the IC has any design, fabrication, or assembly flaws that could lead to 
early field failures. In a few cases, the testing does just that, and some 
built in problem is discovered and corrected. Unfortunately, with highly 
reliable modem linear IC processing, most bum-in failures turn out to be 
bogus. The following list illustrates some of the ways I have seen per- 
fectly good parts "fail" a bum-in when they should not have. 

1, IC plugged into the socket wrong. 

2. Burn-in board plugged into the wrong power supply slot in the 

oven. 

3. Power supply has output overshoot during tum-on, 

4, Power supply sensitive to AC line disturbances. 



2. From image procewing computer programs that combine images. 



The Art and Science of Linear IC Design 

5. Power supplies sequence incorrectly. 

6. IC is inserted in test socket incorrectly after bum-in and gets 
destroyed. 

7. IC fails to make good contact to all bum-in socket pins, causing 
overstress. 

8 . Bum-in circuit allows so much power dissipation that IC junctioii 
temperature is outrageously high. 

9. Bum-in circuit applies incorrect biasing to one or more pins. 

10, IC oscillates in bum-in circuit. (With hundreds of parts oscillating 
on one board, power supply voltages c^ swing well beyOiid their 
Devalues.) 

1 1 , Some parameter was marginal and a slight change during bum-in 
caused the IC to change from "good" to "bad," 

12, IC was damaged by BSD before or after bum-in. 

These twelve possibilities could probably be expanded with a poll, but 
they serve to illustrate a serious problem with bum-in; namely, most of 
the failures have nothing to do with reliability issues. Even one bum-in 
failure is considered serious enough to warrant a complete investigation 
or a new bum-in, so bogus failures represent a considerable waste of time 
and money. Delay in time-to-market can multiply these direct costs many 
times over. 

An IC designer has control over items 7 through 1 1, and these repre- 
sent a large portion of the bogus failures. Considerable thought should be 
given to the design of the bum-in circuit so that it does not overstress the 
part in any way, even if one or more IC pins do not make con^t to the 
burn-in socket. Remember that you are dealing with thousands of socket 
pins which see thousands of hours at 125°C. Some of them will fail open 
through corrosion, oxidation, or abuse. The chance that an open pin will 
be identified as the cause of a bum-in failure is very slim indeed, so you 
must protect the IC from this fate with good design techniques. 

The fully stuffed board should be transient tested if there is any ques- 
tion about oscillations, ICs which dissipate any significant power should 
be analyzed very carefully for excess junction temperature rise. This is 
complicated by the complex thermal environment of a maze of sockets 
coupled to a common board with poorly defined air movement. I often 
just forget calculations and simply solder a thermocouple to one of the 
IC leads. Testing is done with a fully stuffed board in the bum-in oven 
sandwiched in between other boards to minimize air flow. Finally, use 
good judgment to define fail limits so that small, expected changes 
through bum-in do not trigger failures. Many linear ICs today are 
trimmed at wafer test to very tight specifications, and this may necessi- 
tate a more liberal definition of what is "good" and "bad" after bum-in. 

Asking Computers the Right Questions 

Computers are without a doubt the greatest tool available to the IC de- 
signer. They can reduce design time, improve chances of silicon working 



336 



with minimal changes, and provide a reliable means of documentation. 
Computers don't create, but by analyzing quickly, they can allow a de- 
signer to try more nw ideas before settling on a final solution, A good 
working relationship with a computer is critical to many designs where 
classical breadboards are out of the question because of issues such as 
stray capacitance, extreme complexity, or lack of appropriate kit parts. 

A nagging problem with computers is that they only do what they're 
told to do, and in general, they only do one thing at a time. This is reas- 
suring from a confidence viewpoint but it leads to a fatal shortcoming: the 
computer knows that something is wrong with a design, but steadfastly 
refuses to tell you about the problem until you ask it nicely. A particular 
set of conditions causes the circuit to react badly, but those conditions are 
never analyzed by the computer. With breadboards, it is much easier to 
spcA profetems beeaise it is easy to vary conditions even on a very com- 
plex circuit. You can adjust input signal conditions, power supply voltage, 
loads, and logic states over a wide range of permutations and combina- 
tions in a relatively short time, without having to figure out which combi- 
nations are worst case. The results can be observed in real time on meters 
and oscilloscopes. Temperature variation takes longer, but is still quite 
manageable. This ability to quickly push the circuit to "all the comers" is 
invaluable when checking out a design. 

Computer analysis is typically very slow compared to a live bread- 
board, especially on transient response. This can lead to a second hazard. 
The designer knows what analysis he should do, but when confronted 
with extremely long run times, he saves time by attempting to second- 
guess which conditions are worst case. One of the corollaries to Murphy's 
Law states that fatal flaws appear in a design only after the analysis that 
wmtld have detected them is deemed unnecessary. 

How do you select the proper questions to ask the computer to ensure 
that potential design flaws are detected? This decision is critical to a 
successful design and yet many engineers seem very blase about the 
whole procedure and do only token amounts of analysis. They become 
the victims of the lurking flaw and have to cover their butts when the 
boss asks if the silicon problem shows up on simulations. Others waste 
enormous amounts of time doing analysis that generates huge reams of 
redundant data. They get fired when the design is hopelessly behind 
schedule. The following list of suggestions are my version of a compro- 
mise, and limit nasty surprises to those the simulator doesn't predict 
anyway. 

Do a Thorough Analysis of Small Pieces Separately. "Small" is defined in 
terms of computer run time, preferably something less than a few min- 
utes. This allows you to do many tests in a short po-iod of time and forces 
you to concentrate on one section of the design, avoiding information 
overload. Things go so quickly when the number of devices is low that 
you tend to do a much more thorough job with little wasted time. 



The Art and Science of Linear IC Design 



The lowly biasing loop is a good example of why analyzing small 
pieces is helpful. In modem linear IC design, the biasing loops often use 
active feedback to control currents accumtely over wide suf^ly varia- 
tions, or to tolerate variable loading. I have seen many cases where the 
bias loop had very poor loop stability and this did not show up on full- 
circuit transient or small signal analysis. In other cases the peaking in the 
bias loop did show up as an aberration in circuit performance, but was not 
discovered as the cause until hours or days of time were wasted. A simple 
transient test of the bias loop by itself would have saved time and teeth 
enamel. 

Beware of Bode Analysis. Many designers use Bode analysis to determine 
loop stability. This technique has the advantage of defining response over 
the full range of frequencies and it gives a good intuitive feel for where 
phase and gain problems originate. The problem is that with some loops, 
it is nearly impossible to find a place to "break" the loop for signal injec- 
tion. The sophisticated way to inject the test signal is to do it in a way 
that maintams correct small-signal conditions even when large changes 
are made to components or DC conditions. This allows rapid analysis of 
various conditions without worrying about some "railed" loop condition. 
There are many possible ways to inject the signal that accon^sh diis, 
but correct Bode analysis requires that the impedance on one side of the 
signal be much larger than the other overall frequencies of interest. This 
is often not the case, and a Bode plot that seems to be giving reasonable 
answers is actually a big lie. It turns out that the impedance requirements 
typically fall apart near unity gain, just where they do the most harm. 
(Murphy is in control here.) If you have any doubts about the impedance 
levels, you can replace the voltage source with two low- value restst@ts in 
series. Inject a current test signal to the center node and ask for the ratio 
of the two resistor currents over all frequencies. If the ratio is less than 
10:1 at any frequency, the analysis is flawed. (Actually, it turns out that 
there is a way to do an accurate Bode analysis with arbitrary impedance 
levels. This is detailed in Microsim PSpice Application Design Manual, 
but it is a fairly tedious procedure.) Another sanity check is to do a small- 
signal transient test of the loop and compare results with the Bode test, 
(See section on transient testing.) 

A second problem in Bode testing is multiple feedback paths. As linear 
circuits get more sophisticated, it is not unusual to find that there is more 
than one simple loop for the feedback signal to travel. A typical example 
is a bandgap reference where most of the circuitry uses the regulated out- 
put as a supply voltage. Signals from the output can feed back to interme- 
diate nodes in the gain path via load terrrunations and bias loops. This can 
cause some really strange effects, like common emitter stages that have 
zero phase shift at low frequencies instead of the expected -180. It seems 
impossible until you realize that the current source load is changing 
enough to cause the collector current to increase even though the base 



338 



emitter voltage is decreasing. The result is that the net impedance at the 
collector node is negative, and this causes the phase to flip at low frequen- 
cies. The overall loop still works correctly with flipped jAa^ because of 
overall feedback through the normal feedback path. Phase returns to nor- 
mal (-270) at higher frequencies because capacitance dominates imped- 
ance. A second problem occurs at high frequencies where capacitive 
faedtiircmgh in the extra kkops can cause main-loop oscillations. A stan- 
dard Bode plot may not show a problem, whereas a transient test usually 
does. It works both ways, of course. I have seen circuits where the Bode 
plot predicts oscilMons, but the circuit is actually quite stable because of 
a secondary hi^-frequency feedback path. 

Transient Testing Can Also Fool You. I used to think that transient testing 
was a fo0l{^oof way to JvK^e loop stability. It didn't require my interpre- 
tation — either the response looked clean or it didn't. Now I know of sev- 
eral ways to get fooled. The first is to inject the test signal at the wrong 
point or to use voltage when you should use current. There are some 
points in a feedback loop that smoAer the test signal with a low-pass net- 
work that allows only the lower frequencies in the test pulse to get into the 
main part of the loop. The result is a very benign-looking output response 
that does not show dangerous high-frequency ringmg problems. My expe- 
rience shows that this problem almost never occurs if you inject a current 
into a low-impedance node in the loop. Typically, this would be the out- 
put, but a more general guideline is that it be a node that the loop is trying 
to hold to a constant voltage. In a switdiing regulator, for instance, do not 
inject the signal into the post-filter output if that filter is outside the main 
feedback loop. 

A second way to get fooled is to use the wrong test frequency. A loop 
that rings at 50KHz will not look ringy when excited at lOOKHz. This 
may seem obvious, but many loops have more than one frequency where 
phase margin is poor. If you concentrate only on the high-frequency por- 
tion, you might miss that little slow-settling tail that bites you later. 
Likewise, if the test frequency is too low, you might miss a very high- 
frequency buzz that washes out in the screen resolution. A frequent cause 
of these bwzzies is a minor internal loop which has a bandwidth much 
higher than the main loop. Zoom in on edges if there is the slightest hint 
of raggedness. 

Ust1iHII|Mralim tolMrt FNsbUStlim. Sometimes one has to do exhaustive 
analysis of a circuit to prove out the design. You might have to vary sup- 
ply voltages, component values, device parameters, load conditions, logic 
and signal levels, operating frequencies, and on and on. This is very time 
consuming, in some cases much more so than if one had a real breadboaixl 
to test in the lab. When a change is made to the design, one has to care- 
fully consider how much of the previous testing will have to be repeated. 
But engineers are Imman, and when Aey get lazy or rushed, design flaws 



The Art and Science of Linear iC Design 



are missed simply because the designer decided not to repeat a previous 
test after a "tiny" change was made to the design. 

I believe that one way to help ensure a "robust" design is to have the 
computer analyze the circuit at temperatures well beyond the expected 
operating range. The reason this works so well is that temperature has an 
effect on nearly everything in the circuit if the components are niodeled 
correctly for temperature dependeiK^e. This has the desired effect of Vmy- 
ing more than one thing at a time and greatly reduces analysis time, espe- 
cially if you just want to verify that nothing got screwed up by a tiny 
little change. I force the circuit to as many simultaneous worst-case con- 
ditions as I can, then vary temperature from -80°C to -i-200''C to see 
where things fall apart. This usually points out any design weaknesses 
which may be occurring dangerously close to the desired operating tem- 
perature. A good rule of thumb is that the circuit should be a healthy 
25°C below its minimum expected temperature and 50°C above the max- 
imum expected temperature. Circuits which are checked in this manner 
also tend to be very tolerant of those nasty little fab variations that haunt 
all linear designers. 

Look at Transistor Base Currents to Detect Incipient Saturation. Bipolar 
transistor saturation has become more of a problem with modem analc^ 
circuits that have to work at very low supply voltages. Even in older de- 
signs, the collector-to-emitter voltage of an amplifying transistor was 
often the base-to-emitter voltage of a second transistor. This is problem- 
atic because the collector-to-emitter voltage required to avoid saturation 
is proportional to absolute temperature (+0.33%/C), and the voltage actu- 
ally forced on it by a base emitter voltage decreases with temperature. At 
some high temperature these two requirements clash and the result is at 
least partial saturation of the first transistor. For example, if 250mV is re- 
quired to keep a specific transistor out of saturation at 25^C, it will take 
354mV at 150X. A Vbe of 600mV at 25°C will decrease to 350mV at 
ISO^'C. Therefore, at temperatures above 150*^C, saturation will occur. 

Regardless of the exact cause of saturation, the simplest and most 
sensitive way to look for the problem is to plot base currents versus tem- 
perature. A sudden increase in base current at some temperature is a 
good indication of saturation. This is especially critical in precision ap- 
plications, such as bandgap references, operational amplifiers, and com- 
parators. One word of warning: computer models can do a poor job of 
predicting saturation problems when certain model i^rann^ters are ad- 
justed to make other things come out right. Have the computer plot Ic 
versus Vce with constant base current and compare this plot with curve 
tracer readings. Discrepancies will have to be accounted for, or model 
changes made. 

Force Input and Output Signals Beyond Their Expected Range. There are 
all kinds of nasty surprises that can pop up when signals go beyond their 
expected range. The best example is phase reversal in a single si^ly 



340 



input stage. A simple PNP differential input stage with a grounded emitter 
NPN as the second stage will exhibit phase reversal when one of the 
PNPs has zero volts on its base. If the result of phase reversal is that the 
PNP base remains at zero, a nonrecoverable latch occurs. I have seen this 
problem get to final silicon many times because zero volts was not a '*nor- 
mal" operating condition, and the designer failed to consider start-up or 
&ult sieuations. 

A second example is regulator output polarity reversal One normally 
would not expect the output of a voltage regulator to see reverse voltage, 
but this occurs quite often in cases where both positive and negative regu- 
lators are used in a system. If power is delivered to one regulator before 
the other, and loads are connected across the regulator outputs, the pow- 
ered regulator will force the unpowered regulator output to a reverse volt- 
age via the common load. System designers routinely protect against this 
condition by connecting diodes from each regulator output to ground to 
limit reverse voltage to one diode drop. Imagine their consternation to 
find out that thi^ doesn't work with some IC regulators because these 
regulators refuse to start when power is applied with the output reverse 
biased by one diode drop. During simulations, I always force the output 
of regulators to 1 .5V reverse voltage and check for proper start-up and 
full output dWve current. After layout, I check saturated transistors in this 
state to make sure they don't inject to some nearby strucmre that would 
cause problems, a situation that won't show up on simulations! 

Living in Fear of LVceo 

Many linear designers make the mistake of assuming that circuits will not 
work properly if the voltage across bipolar transistors exceeds LVceo 
(latching voltage, collector-to-emitter, with the base open). In discrete 
design, one can simply specify transistors with high breakdown voltages, 
but with a given IC process, the only way to increase LVceo is to reduce 
gain (hFE). More times than I care to remember I have seen fab lines 
struggling to keep hFE in a very narrow range because the circuit designer 
demanded an unreasonable combination of hFE and LVceo. The tmth of 
the matter is that transistors are quite happy to operate well beyond LVceo 
if there is provision to handle reverse base current. The gmph in Figure 
19-1 shows base current and base emitter voltage versus collect emitter 
voltage with emitter current held constant. Notice that nothing spectacular 
happens at LVceo. This is simply the point where base current is equal to 
zero. A transistor with LVceo = 50V and BVcbo = 90V can often be oper- 
ated at 60V to 70V if the design will tolerate a low value of negative hFE 
(reverse base current). Above 50V, some means must be provided to ab- 
sorb the reverse base current, but this is often just a high- value resistor 
across the base emitter junction. At voltages close to BVcbo, reverse base 
current climbs rapidly, and active reverse drive may be needed. 

I have had many designs in production for years, operating well above 
LVceo, with no loss of performance or reliability. There is one caveat 
though: if a transistor is operated at high power levels above LVceo, there 



The Art and Science of Linear IC Design 



Rguret9"1. 

Operation above 
LVceo is safe when 
provision is made 
for reverse base 
current. 




Collector to Base Voltage (V) 

is a danger of forward-biased secondary breakdown, a phenomenon 
where current crowds to one tiny area of the transistor and breakdown 
plummets to half its normal value. This is normally only a problem in 
power transistors subjected to simultaneous high voltage and high cur- 
rent, bat caution should be used in lower-power designs where the tran- 
sistor could be subjected to a transient overload condition. Secondary 
breakdown can occur in less than a microsecond, and unless the voltage 
across the transistor is quickly reduced to well below LVceo, it will be 
permanently damaged. 



Arthur D. Delagrange 



20. Analog Design— Thought Process, 
Bag of Tricks, Trial and Error, 

or Dumb Luck? 



Allow Me to Introduce Myself 

Rather than leave the reader wondering where I got the weird ideas to be 
presented here, and maybe whether I should be allowed to run loose, I 
think it best to tell about my past: I spent my entire money-making career 
doing research and development for the U.S. Government ("the Gov"); 
the Department of Defense, to be exact. None of the authors of the first 
book of this series were in this category, and I will be surprised if any in 
the second are. However, this background does give one a different per- 
spective, which can be useful. 

DOD gets a lot of bad press these days. Most of the accusations have 
some basis in fact, and some are absolutely correct. But the more experi- 
ence I have with industry and academia, the more I see the same prob- 
lems. People are people wherever they are. The laws of physics apply 
indiscriminately to both military and civilian arenas. An idea that does not 
work in one can often be adapted to not work in the other. It increasingly 
seems that when I buy something for home use, I had better be prepared 
to fix it, or even re-engineer it! I am thinking primarily of mechanical and 
electro-mechanical gadgets, for example my daily battles with the car and 
the drink machine (I am not talking about the mornings I sleepily try to 
insert my Exxon card in the Coke machine). Mechanics aside, however, 
the electronics industry is not without fault. I have a car radio that some- 
times emits sounds that are truly awful. There is room for improvement 
all around. 

Given my employment, my experience has been in the design of rela- 
tively simple systems, produced in relatively small quantities, often with 
inadequate development time. I will necessarily emphasize these aspects 
in my philosophy of analog circuit design. My type of work is not as glo- 
rious as designing an integrated circuit (IC) that will be produced by the 
zillions, but it is just as necessary, and applies more often than one might 
think. Examples are: in-house lab equipment that will not be sold or even 
replicated, a jerry-rigged solution to a problem holding up an expensive 
field test, a quick demonstration that a proposed project has a chance of 
working (or doesn't)! 



343 



Analog DeskfrH-Thought Process, Bag of Tricks, Trial and Error, or Dumb Luck? 

The military often makes headlines using a $100 part in place of a $1 
part. (That's 20dB or 40dB, depending on whether you use 10 log or 20 
log. I say use 10 log because money is power.) However, if it would take 
$10,000 worth of testing to ensure that the $1 part is indeed adequate and 
only 100 units will be built, it is a toss-up as to which part is really 
cheaper. Given the horrendous cost of field failure, pick the one that is 
most likely to work. 

Philosophical question #1: Is an inexpensive widget that does not work 
better than an expensive one that does not work? You can buy more of 
them, but so what? 

Philosophical question #2: If you were going into battle and your life 
depended on your equipment, which you didn't have to pay for, would 
you pick military or commercial? 

The military (and NASA!) are extremely concerned about reliability; 
failures may be spectacular. So is industry; a design failure could easily 
mean a recall of 100,000 cars for General Motors. There is an ongoing 
discussion (argument, really) of how to achieve reliability. It is not likely 
to be settled soon, especially given that we have not agreed on exactly 
what constitutes failure! 

Problem #1: Supplier As widget meets all specs, but just barely in every 
case. Supplier B's widget is right on target in all cases except one^ where 
it is unfortunately slightly out of spec. Which would you pick? Hint: the 
Gov picks A. 

Problem #2: As you get farther from the transmitter, FM radio sounds 
great out to a point then drops out rather suddenly, while AM just gets 
noisier and noisier. Which is better? Hint: good music stations are on FM; 
emergency broadcast information is on AM. 

A couple other items: I taught a course on Applications of Analog 
Integrated Circuits for ten years, mostly to sUidents who weren't terribly 
interested, I know that some people don't get excited when they see an 
analog circuit, even a beautiful one. I learned which concepts were easy 
to pick up, and which were difficult. After it was all over, I realized I had 
never specifically mentioned one of the most important aspa<^^ of Malog 
design — it is FUN! Too many digital projects consist of taking an arbi- 
trary bunch of nuntf>ers and performing some questionable calculations 
on them in order to produce something I am not really interested in. I 
liken it to that marvelous invention, the kitchen compactor, that takes 20 
pounds of garbage and transforms it into 20 pounds of garbage. I get the 
feeling the only time the bit flippers get any excitement is when the sys- 
tem crashes. I am not totally against computers; I enjoy playing back my 
phone messages and hearing my answering machine having a discussion 



344 



Arthur D. Del£^i^ 



with some store's computer. I don't know about artificial intelligence, but 
they definitely have artificial stupidity! Pages of ones and zeros just don't 
excite me. (An exception is my checking account; that's close enough to 
reality to get my attention.) Digital design will soon be just computers 
designing more computers, if it isn't already. 

Analog, on the other hand, does not seem to be amenable to automatic 
design. And it usually has to connect to the real world. You hook up your 
new amplifier and get the joy of observing sounds coming out of your 
speaker; or smoke, depending on your level of expertise. Pushing a button 
on a transmits ycwi've designed, hearing the acoustic pulse go out, then 
feeling the earth shake under your feet as 50 lbs of explosive go off is an 
experience unmatched by anything I've seen in amusement parks. 

Computer designers don't know what to do with a good op amp; in 
fact, there is nothing they can do. We analog people get to play with all 
sorts of neat stuff, including digital circuits! In reviewing 20 or so sys- 
tems I've designed, I found that not one was free of digital circuits! In 
fact, half the time it was not clear whether the system was predominantly 
analog or digital. But we get to count these as analog! 

If you read Bob Pease, you know that some of the world's most sophis- 
ticated measuring equipment (his) relies on such high-tech items as card- 
boaixi boxes, spray paint, dishwashing soap, plastic scraps, and RTV 
silicone glue (use electrical grade; some of the regular type contains 
acid!). To that I would add; Reynolds Wrap, duct tape, paper clips, refrig- 
erator magnets, and Coke cans. 

Lastly, I claim to be an expert on mistakes, for the simple reason that 
I've made most of them already, and am working on the rest. When I 
advise against something, it's usually because I've already tried it, with 
disastrous results. 

I have never really been able to explain how I go about designing 
something, and doubt that I ever will. Nevertheless, Table 20-1 gives 
some aspects that are involved. These are not steps in the sense of finish- 
ing one, then going on to the next. They overlap, and one should try to 
keep all of them in mind at all times. I will ramble through these; you will 
see that many items could have been placed in more than one section. 



tiiiliaiH Sfe( *^q^" to Analog De^ 

1 . You want me to what? 

2. A better mousetrap — ^because the mice are getting better. 

3. Breadboard — ^the controlled disaster. 

4. If it doesn't work, take two capacitors and call me in the morning. 

5. Look, Mom, no smoke! 

6. The job's not ov^ till the paperwork is done. 

Note; I will not attempt to distinguish between small systems and large circuits; with ICs there is a 
lot of overlap. A switched-capacitor filter may be listed as a circuit, but you better be aware of 
Nyquist's theorem, which is really system theory. Do not attach undue significance to whether 
**circuit" or "system" is used in any given place. 



345 



Anat^ Ctengn— Thought ProcMs, Bag of Tricks, Trial and Error, or Dumb L\uM7 



You Want Me to What? 

First, make sure the problem is clearly defined in your head. This is so 
obvious it often gets overlooked. Did you understand clearly what your 
supervisor wanted? Did he uncterstand what the customers wanted? Did 
they understand what was really needed? You will not likely get many 
brownie points for doing exactly as told if what you were told was idiotic. 
In the Gov, engineers are not allowed to talk to prospective contractors to 
answer questions during negotiations. I understand the legal reason — ^to 
prevent favoritism — but technically it's exactly backwards. One of three 
things usually happens: 

1. We talk with likely contractors before the bidding starts. 

2. We talk during the bidding anyway, with the warning that, 'T am 
not allowed to talk to you; you are only imagining that I am; if 
asked later I will not remember any of this." 

3. There are monster misunderstandings. 

It is sort of like designing an op amp circuit without feedback; i.e., 
impossible. It is my view that engineering implies getting something 
done, and if that requires bending the rules into a triple granny knot with 
a half hitch, so be it. 

Once you understand the goal, don*t lose sight of it. I once fiddled with 
a circuit until I had a very efficient form, and gleefully presented it to my 
supervisor. He agreed that it was very efficient, but pointed out that it 
performed the wrong function. I had gotten so engrossed in the details 
that I had lost the big picture. 

I do not mean to exclude pursuing a tangent, or even idle dreaming on 
your own; that has led to several of my inventions. But once a tangent 
becomes promising, make it a secondary clearly defined goal Ants accom- 
plish quite a lot with their Brownian motion, but they haven*t designed an 
analog circuit yet, not even a digital one! 

A Better Mousetrap^ecause the Mice Are G^ing 
Better 

This used to be a joke, until I read that the Gov is trying to breed better 
mice. Just what we need, right? My cat can't catch the ones we have now. 
. . . Anyway, the next step is to get started toward your now clearly de- 
fined goaL Getting started right is important; speed is not terribly relevant 
if you're headed in the wrong direction. False starts are inevitable, but 
admit them early. Maybe you have trouble getting started; I do. Selecting 
the best idea from all the ideas in the world, thought of and not thought of 
yet, overwhelms me. But fear not: 

AXIOM: 

There may be an optimum system, but you don't want it. 

346 



Arthur D. Dek^r^e 



A system can be optimized for one, maybe two, variables only, at the 
expense of all others; maybe serious expense. Furthermore, maxima are 
usually fairly broad and flat-topped, so normally you can move a ways off 
the peak without losing much, possibly gaining a lot on another variable 
wtere you ware way down the slope. 

Hypothetical problem: You want to maximize two functions, one 
proportional to cos q and the other to sin q. You shouldn't need 
higher mathematics to tell you it's impossible. One method of at- 
tack is to decide which is more important, let's say the cos one, and 
maximize that. At q = 0 cos q = 1, 100%, but sin q = 0, zip, nada, 
-oc^dB. Oops. But by moving out to q = 0.3 rad, you can have sin q = 
03 and still have cos q = 0.95; or to q = 0.5 rad and still get sin q = 
0.5 and cos q - 0.9. Not bad, huh? 

Similar problem, different subject: When adjusting a tuned filter, 
don't try to "peak" it. The response changes very little around the 
peak. Adjusting for zero phase shift is a far more sensitive method. 
If you can't do that, it is also more accurate to adjust so the 3dB 
down points straddle the desired center frequency. 

OTHER AXIOM: 

If you've done the job, it's done. Sort of. 

There isn't much reward for reinventing the wheel. However, a guy 
named Rader invented a new type of wheel, and if he got a patent, he 
should have a lot more money than I do. The obvious starting point is: has 
the job been done before? If not, is there something close? Table 20-2 
gives my favorite sources for ideas. 



Source Comment 

Personal memory The mind is pretty good at remembering and 

correlating patterns. 

Others* memory Two heads are better than one, if they're on different 

people. 

Mfrs' spec sheets and Usually work, use available devices, assistance 
application notes available. 

Magazine articles I clip any that might be useful and keep them in a 

notebook. 

Textbooks Optional; good ideas usually show up in above 

items. 

Patents May be necessary anyway to avoid paying royalties 
or fines. 

Note: decreasing order of importance 



347 



Analog Destgiv-Thought Process, Bag of Tricks Jrial and Error, or Dumb Luck? 

Be aware of conventional wisdom, but don't be limited by it. An inven- 
tor, whose name nobody remembers, worked on a telephone before Alex- 
ander Graham Bell, but was advised that the telegraph was perfectly 
adequate. Things are done the way they are for a reason, but it may not be 
a very good reason. Feel free to find out. Wear safety goggles, or at least 
some kind of glasses. Ordinary plastic lenses will stop most types of elec- 
tronic shrapnel. Life is dull if you follow the instriKJtions. 

Back in 1966 we needed a sample-and-hold with a very long hold 
time. This implied a buffer with a very high input impedance. (^Capaci- 
tors are only available so big, especially ones that have low seH^teafeage.) 
MOS transistors had become available, but "everybody knew'' they were 
unstable, noisy, and susceptible to damage from static electricity. How- 
somever, they were so cute I couldn't resist. I figured out how to make a 
reasonably accurate buffer Temperature stability wasn't good; in fact, if 
you got the device too hot the characteristics changed permanently! But 
the circuit was to be used in a controlled environment. It was a PC appli- 
cation, so I could beat down the noise with capacitance on the output. I 
did lose a few MOSFETS through careless handling, but once in the cir- 
cuit with a microfarad on the gate, they were safe. I don't recall the exact 
hold time, but I know I measured droop by sampling a voltage one day 
and measuring it the next! At first it looked like the hold time was infinite, 
at least until I realized it drifted toward max voltage, not zero. . . . The 
reader should wonder what switching device was good enough; it was a 
relay! 

I published the circuit* and there must have been considerable interest 
because I received a dozen or so inquiries. Later RCA succeeded in mak- 
ing IC op amps with MOS transistors. These were pretty much pooh- 
poohed because the input specs weren't good, but look at the variety of 
CMOS devices available now! 

Adapting an old idea has the advantage that you are starting with 
something that presumably worked, but be aware of: Pitfall #1 : A good 
idea applied to the wrong situation is a bad idea. Pitfall #2: Murphy's 
Law, applied to drugs, adapted to circuits: Any modification which pro- 
duces a good effect will also produce numerous bad side effects. 

Seldom are two applications identical. Some subtlety may trip you up. 
The Band- Aid approach has its hmits. Exception: politics. A few years 
back our laboratory got no money at all for new construction, but a siz- 
able pot for alterations. They took a tool shed, added three wings and an 
upper story, and made a respectable building out of it. The original build- 
ing became the foyer. It had to retain its "T" number, "T" meaning 
Temporary (since 1945), but who cares? I have designed new equipment 
with very strange nomenclature borrowed from other equipment to avoid 
running afoul of some rule. Use your imagination. 



348 



Arthur 0. Deti^range 



Look at ft Anotlier Way 

Very often the solution to a problem appears immediately upon formulat- 
ing the problem differently. I like to recall a story I read of moiuitain 
climbers who attacked a lesser but still-unclimbed peak. They reached a 
huge chasm and had to turn back. They related the information to another 
party who tried a different route and went right to the top. If they instead 
had tri^ to best the chasm, the mountain might still be unclimbed. 

Example: The standard way to measure phase difference is to set a 
flip-flop on the zero crossing of one signal and reset it on the zero cross- 
ing of the other. The fraction of the time that the flip-flop is set gives the 
fraction of a <qrcle the second signal lags the first; averaging and scaling 
gives a DC readout of 0 degrees to 360 degrees. This gives an ambiguity 
at 0 = 360. Phase jitter around zero gives an average readout of 180 de- 
grees, exactly wrong! This is normally solved by adding 180 degrees by 
inverting one signal, moving the ambiguity to 180. But we had to build a 
phaaemeter into a hands-off system, where the necessary automatic 
switdung would have added considerably to the complexity. The solu- 
tioti was to measure the angle in sign-magnitude format (0 to 180 de- 
grees, plus or minus), which has no ambiguity. The circuitry for this 
method turned out to be fairly simple, also,^ and had an additional ad- 
vantage for unattended oper^on: a modest amount of noise caused 
only a modest error; extra zero crossings can drive a set-reset phaseme- 
ter crazy. 

Sometimes you have to reverse your thinking entirely. The standard 
way of protecting against reverse battery connection is a diode, but the 
voltage drop is sometimes unacceptable, I, and probably many others, 
tried unsuccessfully to do it with a power MOSFET. The obvious way 
doesn't work because the inherent back diode conducts when reverse 
voltage is applied. Bob Pease got a patent by realizing all you have to 
do is turn the transistor around backwards! The FET doesn't really 
mind, and the back diode is working for you! 

Bag of Tricks 

Certain concepts appear over and over again. I like to think of them as a 
bag of tricks, in the sense that a magician's "tricks" are really scientific 
principles, skillfully applied, with special attention to how the human 
brain works (and doesn't work). Here are a few of my favorites: 



349 



Analog Design^Thought Process, Bag of Tt^icks, Trial and Error, or Dumb Luck? 



PLLs and FLLs 

Phase-Lock-Loops (PLLs) are cute devices, widely used, even where they 
shouldn't be, A similar device, the Frequency-Lock-Loop (FLL)^ has 
some features the PLL does not, at the expense of giving up some you 
may not need in a given application. Possible advantages are: no out- 
of-lock state and hence no lock transition; insensitivity to phase inver- 
sions or even arbitrary phase jumps; frequency can be offset in a linear, 
continuous nmner. The two devices together cover a wide range of appli- 
cations. For an example, read on: 

Frequency Syirth^^l^ Many systems need one or more accurate fre- 
quencies. Even the crystal manufacturers themselves don't stock all pos- 
sible frequencies; it's prohibitive. They will cut any frequency for you, 
which will necessarily cost you more and take considerable time. And 
what if you need to switch the frequency? An indirect frequency synthe- 
sizer takes a reference frequency (e.g., from a standard crystal oscillator) 
and multiplies it by one arbitrary integer and divides it by one or two 
others.^ It uses a feedback loop (a PLL) and some counters. Thus you 
can take one accurate frequency source and create a host of others semi- 
digitally. Often there is an accurate clock around; even microprocessors 
have crystals attached these days! There are some design techniques you 
need to know and some limitations, but they are not bad. I have these in 
half a dozen systems. 

Tone D^ectOfS What if instead you have to detect a signal of known fre- 
quency? Generate the expected frequency with a synthesizer, then com- 
pare the input signal with it in a simple circuit (see also Note 4). The 
center frequency and effective bandwidth, and also the shape, of the ef- 
fective bandpass filter can be precisely controlled. Frequency hops can be 
programmed. I have used this in several systems, too. 

Pseudo-Noise Pseudo-random noise (PRN or simply PN) generators'-^ 
generate a neat signal that looks like noise, but is actually deterministic, 
and hence has precisely defined properties. They are made from a few 
shift registers and gates, possibly followed by filtering. Why generate 
more noise, when we are plagued with enough of it already? Well, noise 
testing for one thing. Secure communications for another. And how else 
do you generate a reasonable broadband signal? 

MocHitatlon/DeillOdulatto^^ When I say "modulation/' you prob^y think 
radio or TV. But it is useful in a surprising number of other applications. 
Chopper op amps use modulation. It can be used to do some fancy filter- 
ing tricks; how about a 60,000dB/octave filter?^ Need narrowb^d 
noise? Use a PN generator, filter the output to the exact shape and (half) 
bandwidth you want, then modulate it up to the desired center 
frequency ! 



aso 



Arthur D. Det^range 



Sine and Triangle Generators Generating a sine wave is one of the classic 
problems of our discipline. Some really terrible ways of doing it have 
b^n devised. You cm take a microprocessor and a D- A converter and in 
less than a year generate a stairsteppy thing that looks like a sine wave if 
you stand across the room. Unless you really need a tow-distortion sine 
wave, just generate a square wave and remove the harmonics with a 
low-pass or bandpass filter. Triangle wave? Just run the square wave 
through a pseudo-integrator. If a square wave isn't already available, you 
can get it from the triangle wave itself with a hysteresis clipper (Schmitt 
Trigger). (One of the two circuits has to invert.) This makes a loop and is 
the basic function generator circuit. 

Thevenin and Norton Equivalents; Frequency and Impedance 
Tram^rmattons 

These "tricks" can simplify a lot of problems and allow you to juggle 
circuits into more desirable forms. They should be in any good circuit or 
filter book; if they're not in yours, trash it and I'll send you mine,^ From 
time to time an article appears on how to build gain into a filter stage, 
usually using a computer program. It is not necessary.^ The filters of 
Figures 20-1 A and 20-1 B have the same characteristic; only the gain is 
different. In both cases the open-circuit voltage (mentally break the loop) 
at el is equal to e2 but comes through an impedance of C V2. (For any G, 
the two capacitors to the right of the dotted line in Figure 20- IB sum to 
C ^2.) The circuit to the left of the dotted line does not know what is on 
the right side (unless it peeked). Hierefore, for any input the voltages at el 
and e2 will be the same in either case. The output is simply e2 multiplied 
by whatever gain the op amp is set for by the negative feedback divider. 
As a quick check, let G go to zero; the circuit of Figure 20- IB reduces to 
th^ of Figure 20-1 A (with an extraneous load resistor). 

If all capacitors in the circuit of Figure 20-1 A are increased by a factor 
X (Figure 20- IC), it should be obvious that the time response to an im- 
pulse will have the same shape, but will be expanded X times (slower). 
Since the frequency response is the Fourier transform of the impulse re- 
sponse, the frequency characteristic retains the same shape but is com- 
pressed by a factor X in frequency. This also should tell you that all 
capacitors in a filter should be of the same type so they will drift together 
The cutoff frequency will necessarily drift, but at least the filter shape will 
not change. In fact, when building the circuit of Figure 20-1 A, instead of 
looking for two similar capacitors whose values differ by exactly a factor 
of two (which seldom happens), I get three of the same value, hopefully 
from the same lot, and parallel or series two of them. 

I once had to design a sinusoidal oscillator of frequency 0.004Hz. 
That*s a period of about four minutes. And it took at least 10 cycles to 
settle after power-up. After running a few strip-chart records I realized I 
might not live long enough to complete the design. I got smart and re- 
duced the capacitors by a factor of 1000, Using a 'scope, I got the bugs 



351 



An^og Design— ThougM Process, Bag of Iticks.Tt'ial and Error, or Dumb Luck? 



Figure 20-1. 

Gain, frequency, 
impedance manipu- 
lations on a 
Butterwortli filter. 




r 

yc_^ 




out of the design in about the same time it previously took to make one 
adjustment and check it. Then I reduced the capacitors by factors of ten, 
making sure no side problems cropped up. This works for high-frequency 
filters, too. Get the circuit working correctly at a frequency where the op 
amps are nearly ideal, then start reducing the capacitors and watch the 
effects of finite gain-bandwidth (and stray capacitance) show up! 

If all the impedances in the circuit of Figure 20-lA are reduced by a 
factor Y (Figure 20-lD), the voltage transfer ratio is unchanged, since 
voltage transfers are determined by ratios of impedances. The input im- 
pedance is indeed Y times lower, but remember, I said voltage transfer 
ratio. This allows the three capacitors in my version to be juggled to a 
power of ten; oddball precision resistors are easier to find. There are other 
things that can be done, too, but they take a little more math. 



3S2 



Arthur D< Derange 



SMf^ from Scratch 

How does one generate an honest-to-goodness, brand-new, out of-the- 
blue idea? I can see steps leading up to it and numerous altem^ives dis- 
carded, but I can't explain the spark, the actual jump from the old to the 
new. Let me walk you through some of my favorite creations: 

I was working with elliptic filters, which require zeros. I could not find 
a single op amp filter section having zeros in any of my books, so I in- 
vented my own. (As far as I know; I have since run across two others, but 
both are more complicated than mine.) EUiptics are relatively easy with 
passive filters — the impedances of a capacitor and an inductor are equal 
but opposite at some frequency; cancellation produces a zero. (Skip ahead 
to Figure 20-4 if necessary.) I reasoned that the differential inputs of an 
op amp could do the differencing, or subtraction. If the input had two 
paths to the output, via the two op amp inputs, which had the same volt- 
age divider ratio at some frequency, the output should be zero at that fre- 
quency. It would have to be in order to maintain zero voltage across the 
op amp inputs. The one path could provide the negative feedback required 
by the op amp, and the other could provide the positive feedback required 
for filter peaking. 

In reviewing frequency-selective circuits, I noticed that the Wein 
bridge, used as a voltage divider, had phase lead at low frequency and 
phase lag at high frequency (or vice versa, depending on which end you 
look at). Somewhere in between, phase shift had to be zero. I did the 
equations, and, sure enough, at one frequency it looks like a 1^-% voltage 
divider with no phase shift. Now I was excited. 

This would give me a pure notch, with equal amplitude on either side. 
This was not exactly what I needed, but I could probably fudge one end 
or the other to get different amplitudes. I thought of several possibilities; 
the most promising was that I could split off part of one capacitor or re- 
sistor in the Wein bridge, using Thevenin equivalents, and not alter the 
fundamental properties of the bridge. The end result is shown in Figure 
20*2. It seems pretty minimal for all it has to do. There are no obvious 
nasty requirements on the op amp. But hold on; there is more! 

I was fascinated that at one frequency the op amp output did exactly 
nothing. It was a true zero; there was no approximation in my calcula- 
tions. Did I really need an op amp, or would any old differential amplifier 
do? I would still need positive feedback, but why couldn't that work, too? 
It did work (Figure 20-3)! Heady with success, I pushed on. One by one I 
took the standard op amp circuits and converted them to "diff-amp" cir- 
cuits. Who needs gobs of gain? Who needs op amps? 

My revelation to the world generated a tidal wave of apathy. Overnight 
I was propelled from obscurity to oblivion. 



353 



Analog Design— Thought Process, Bag of Tricks, Trial and En^or, or Dumb Luck? 





A. BASIC CIRCUIT 



His) 



S^ + AS+B 



COMPGNEr'T VALUES 



Figure 20-2. 

Single op 
anp resonator 
with zeros. 
(Appeared in EDA/, 
24 January 1985.) 



HIGHPASS 



LET /J 



1;C,=C2 = l 
D 

(1-B) 



G = 



1 



(R,+R^- B ) 



"^SERIES 



^SHUNT 



^1 

D 

G + B 
G-Hl 

R, 



LOWPASS 



LET a = 1;R, =R2 = 1 



C, = 



G = 



B^ 

(1- D) 



1 

BCl 



(C^+Cj- B) 



P = 



"SERIES 



"SHUNT 



IB 

G+D 

G + 1 



(1-/J)Ct 



POSTULATE: 

Ideas, akhough having no mass, do have inertia. They are hard to get 
going, but once moving they are hard to stop. This applies to both good 

and bad ideas. 

Although probably ancient history by now, here's another example of 
what can be done with a little cleverness: I needed a fairly sharp 5KHz 



354 



FILTER FUNCTION 


FORMULA 


d 


G 


^SER 


^2 




^SER 


C2 


^SHU 


POLE-ZERO QUAD. 
LOWPASS WITH 
IMAGINARY ZEROS 


D>B 


1 

1 


A 

3- 


1 


1 


NONE 


1 3 

i2 - 1 


1 


1 3 

{ -V 


+ As + B 


2 + B/D 


/B 2 + B/D 


7b 


vHff 2 + B/D 


POLE-ZERO OUAD 
HIGHPASS WITH 
IMAGINARY ZEROS 


D<B 

s^ + As + B 


1 

1 - ~ 

2+D/B 


A 

3- 


^ 3 
2+0/8 


1 


3 

- 1 

2 + D/B 


1 


1 


NONE 


POLE-ZERO QUAD, 
NOTCH 


S^ + B 
s^+As + B 


2/3 


A 

3- 


1 


1 


NONE 


1 


1 


NONE 


POLE-ZERO QUAD. 
ALLPASS 


3^-A$+B 
a^ + As + B 


1 

1 - 

3 + A/vnff 


A 

3- 






NONE 


1 




NONE 


POLE-PAIR 

SINGLE-ZERO, 

BANDPASS 


s 

a^ + As + B 


1 


A 

3 




1 

7i 


NONE 


1 




NONE 


POLE-ZERO PAIR, 
ALLPASS 


s-1 
s + 1 


1/2 


DOESN'T 
MATTER 


1 


NONE 


NONE 


NONE 


NONE 





Figure 20-3. Resonator with zeros with no op amp. (Appeared in EDN, 20 February 1986.) 



Analog Design— Thought Process, Bag of Tricks, Trial and Error, or Dumb Lucic? 



Figure 20-4. 

Passive low-pass low-pass filter; three of them in fact, fairly well matched in both ampli- 



tude and phase. I started out with the passive filter shown in Figure 20-4, 
without the asterisked inductors. Although somewhat of an antique, this 
filter met my needs and had a lot of nice properties: amplitude is reason- 
ably flat across most of the band, phase is pretty linear across most of 
the band, it has a nice steep roUoff which can be changed by adding or 
deleting LCs without changing the others, and it is not paardcularly sensi- 
tive to any one component. It was quite compact, using subminiature 
inductors. Lastly, it requires little thought, an advantage for some of us. 

The main problem was th^ the winding resistance of the inductors was 
rather high. (Just wait till they get room-temperature superconductors!) 
The resistance of the first inductor could be subtracted from the input 
resistor, and the resistance of the last inductor from the terminating resis- 
tor (giving only an additional fixed attenuation), but that still left a bad 
one in the middle. I investigated converting the passive ladder lo active by 
synthesizing the inductors. They were "floating*' (neither end grounded), 
which was bad. Then I read about the "super-capacitor" transfofma- 
tion.^^^2 If you change inductors to resistors, resistors to capacitors, and 
capacitors to super-capacitors, the voltage transfer function is unchanged! 
(Remember the old impedance transformation trick?) And the inductors 
are gone! Don't look for super-capacitors at Radio Shack; they aren't two 
terminal devices. (Physics says they can't be.) Each requires a circuit of 
two op amps, two capacitors, and some resistors. Super-capacitors are also 
called Frequency-Dependent-Negative-Resistors (FDNRs) because the 
impedance is resistive, not reactive, but carries a minus sign. (Don't con- 
fuse these with the new ultra-high-capacitance double-layer capacitors, 
which unfortunately sometimes also are called "super-capacitors.") 

I had my doubts about such hocus-pocus, but tried it. With the addition 
of a couple of resistors to provide DC bias for the op amps it worked, and 
the resistors could be arranged so as not to affect the filter response at all! 
Getting rid of the non-ideal inductors improved the actual filter character- 
istics. It had cost me a quad op amp and a few resistors, but in the appli- 
cation it was a good trade. 

I found a couple more tricks. I had discovered that varying the termi- 
nating resistors (in the passive version) would improve one part of the 
frequency response curve at the expense of some other part. The resistors 
obviously should be frequency dependent. That sounded vaguely famiHar. 




356 



Arthur OD^apMge 



Sure enough, what I needed was a pair of super-inductors; worse yet, one 
floating. But that was in the passive version; in the active version they 
reverted to ordinary inductors! After all that trouble to get rid of induc- 
tors, should I put two back in? Yes indeed! It reduced the droop at the 
bandedge noticeably. Since they added just a minor correction, they were 
not critical; and the winding resistances could be subtracted from the ad- 
jacent resistors anyway! 

There was still some "fuzz" on the output signal, as the system used 
tones at 7.5KHz and 15KHz. Making the filter an eUiptic-like would be 
easy in the passive ladder; you just add inductors in the shunt legs to 
create the trMsmission zeros (refer back to Figure 20-4). And in the ac- 
tive version it meant adding resistors, a virtual freebie! (Note that this is 
not a true elliptic; if you place the zeros at specific places, the humps in 
the reject band will be unequail.) The zeros did increase the sag at the 
edge of the passband, but I could minimize this by toying with the two 
terminating inductors some more. 

The overall circuit is shown in Figure 20-5 and the response in Figure 
20-6. It has proven quite satisfactory. Note that the precision capacitors 
are all equal and have been juggled to a nice value using impedance trans- 
formation. Passive-derived filters can be hard to troubleshoot, as they 
cannot be split into independent sections. I had one that met spec, but de- 
finitely looked different from the adjacent two. I found an op amp shorted 
to ground; the sensitivity was so low it worked with a part missing! In the 



Figure 20-5. 

Active version of 
low-i:)ass ladder. 



— 1 1 — -t — ✓vv-^jryji. 



SUPER- 
CAPACfTOR 




— xAAr— 



I 



r 



•NECESSARY FOR DC 
CONTINUITY; (OOKfU '% 



ALL CAP$ 



357 



Figure ^>-6. 
Gain and phase 
response, active 
version of filter. 




FREQUENCY (KHz) 



Arthur D. DeiaiH^aiige 



elliptic-like, however, the shunt legs can be easily checked. The voltage 
across each leg should drop to zero at the frequency of the zero it creates. 
Once ttese are working properly, theie isn't much left to check. 

Would I do it again? Probably not. Today you can get elliptic filters in 
mini-DIPs, thanks to switched-capacitor technology, and these would 
probably do the job and have better matching. Engineering consists 
mostly of trade-c^s; you usually don't get something for nothing. 
However, there are some "freebies." Be on the lookout for them; they are 
pearls of great price. We are lucky to be in one of the few businesses 
where new devices not only work better than the old ones, but are likely 
to be less expensive, too! 

BiMdbo^tl^he ControHed Disaster 

If there is one point that is central to my design method, the focus, the 
peak, it is the breadboard. I mostly design by making mistakes and then 
correcting them. I don't particularly recommend this method, but it works 
for me. I don't think I would have succeeded in a discipline where I 
couldn't test my ideas. I think on paper; I don't even like to answer the 
phone without paper and pen in front of me. After the basic design, I 
think directly on the workbench. That hairy rat's-nest with a bunch of 
leads connected to it is very important. 

Exception: When I work with the explosives people I am a lot more 
careful. Aside from the possibility of drastically reducing local real estate 
values and putting one's self into low earth orbit, a single accident can 
mean the end of a project. Even if no one gets hurt, it is obvious someone 
could have. There are other areas tiiat r^ire extra caution: high- voltage 
or high-power systems, radiation, naedicd electronics, equipment des- 
tined for Mars , . . 

I recently had to design a system involving magnetics, a subject I had 
been able to avoid since college. I came up wiUi a system that worked 
great — in my head. I wound one coil on a Goke can and another on a 
piece of roofing flashing. They didn't work worth beans. I scratched my 
tead until I remembered why coils aren't wound on ^uminum forms. 
Although aluminum is not magnetic, it is conductive, and those cylinders 
looked like one-turn secondary windings, shorted. I tried it again with a 
plastic wash bottle and a glass beaker, and it worked 1000% better, ff I 
had m^e drawings and waited for cylinders to be machined, I would 
have wasted a lot of time and money. 

When I had to get a signal off a rotating drum, I wondered why I 
couldn*t just insuMe the ball beings on the shaft and run the signals 
through them. I dug a couple out of my junk bin, rigged them up, and 
immediately found out why people use slip rings. The bearings generated 
almost a volt of noise! 



3S9 



Analog Design— Thought Process, Bag of Tricks Jrial and Error, or Dumb Luck? 



Push-in breadboarding strips have been much maligned. I agree they 
are not the way to go for state-of-the-art design* but for mundane work 
they are great- 1 have some laboratory boxes where* if you take the cover 
off, you find a push-in strip inside! Just use common (engineering) sense. 
You don*t leave inch-and-a-half leads on the components on a circuit 
board; why should you expect to get away with it on a push-in strip? 
Ground unused strips. Put an old metal panel underneath as a ground 
plane (connected to ground* of course). Whene possible* connect strips 
adjacent to sensitive points to guard terminals (low-impedance points that 
are nearly the same potential). Clip off unused IC terminals; don't count 
on them being unconnected inside, I recently published an article on a 
fairly fast circuit," The 'scope trace was unfortunately left out; it is shown 
here as Figure 20-7, Note that the output rise time is 20ns, It was done on 
a push-in strip. 

At least nine times out of ten the circuit card will work better* which is 
nice. But watch out: 



WARNING: The layout is part of the circuit. 



Figurtt 20-7, ^ designed a crystal oscillator on a push-in strip. I ran it through a wide 
Response of wide- range of temperature and supply voltage with no problems. But when we 
band transconduc- put it in a fancy hybrid circuit* some units intermittently oscillated at a 
tance amplifier 

differentiator. 



stopped 



DISPLAY 





1 








r 

\ _^ 












i 














' j 


























i 


























1 




















If 


















V 

^ 1 

.1 











norm 



env 



0 



« of avg 



of screens 

n 2 



1 



off 


f r 0 rn e 


axes 


■ grid ■ 



connect dots 

■sn 



-500.000 ns O.OOCOO 3 500.000 1 

100 ns/div 

acVnusC 1 ) 60.653 mv frequencyt 1 ) not found 

9cVrirtsC2J 167. lyOmV frequencyC 2 ) I, 192861m 



display record 
extended 



ed 



Sensitivity Offset Probe Coupling 

Channel 1 50.0 nV/div 0,00000 U 10.00 :1 ec (IM ohn> 

Channel 2 50-0 nU/div 0.00000 U 10.00 :1 ac < til ohm) 



Arthur D. De^^ange 



much higher frequency. I couldn't make the breadboard do it. I guessed 
that the circuit liked the extra stray capacitance of the breadboard. This 
seemed consistent with the breadboard version refusing to go high. I esti- 
mafed the stray capacitance on the output, experimentally found the max- 
imum the circuit would tolerate, and picked a value in between. Adding 
this to the hybrids fixed them all. 

Being able to hwufcoard has a number of caieer-enhancing advan- 
tages. When a question comes up, I can go to my bench and get the an- 
swer. And it's the real answer, not what I think is the answer, or what 
some computer thinks is the answer. The projects that get done are the 
projects that get funded. The projects that get funded are the projects that 
get approved, normally done at a managers' meeting held in a room with 
no windows to the real world, Uterally or figuratively. Computers these 
days can make some pretty fancy vu-graphs, but when I pull a b'eadboard 
out of one pocket and a battery out of the other and hook them up and put 
on a demonstration, it's no contest. 

WARNING: 

Don't put the battery in the same pocket as the circuit 

I did this once, and as I pulled the circuit out of my pocket, the flash- 
bulb went off . The circuit had somehow made contact with the battery 
and powered up. Bad demonstration. 

ALTERNATE WARNING: 

Eton't put the battery in the same pocket as the car keys, either. 

Again, against all odds, the battery made contact. This gave a whole 
new meaning to the term "hot pants." 

On an acoustic link we developed, I had the project manager take the 
receiver downtown to the sponsor, lay it on his desk next to the speaker- 
phone, call me back at the lab, and tell me what code he was setting it on. 
I set the transmitter to that code, laid the phone beside it, and sent the 
tones. A flashfelb went off in the sponsor's face. Now, granted, the phone 
company does this sort of thing all the time, but it still makes for an im- 
pressive demonstration, showing that your idea really works. 

In the Gov we are not supposed to work on anything until the money 
arrives, which, due mostly to Congress, can be nearly at the end of the 
year. But the deadline for completion never shifts with the delay in fund- 
ing. Also, it seems that THE ANSWER is always needed by COB (Gov- 
emmentese for Close-Of-Business). Whether it be the value for a resistor 
or the meaning of life, it is necessary for a meeting the next morning. 
Therefore, my systems usually have to be designed with parts on hand; 
there isn*t time to order some. The best I can hope for is to upgrade later. 
This makes the following item important: 



Analog D^tgrh-Thought Process, Bag of Tricks Jrial and Error, or Dumb Luck? 

My Private Stock 

Table 20-3 gives a summary of what I try to keep on hand, and why. Do 
not try to buy everything in the world, especially all at once. My rules for 
getting parts are 

1. When ordering a part, order extra so I'll have some next time. 

2. Order a diflferent part, too; one I think I might need in the future. 



Table 2(M Stock of Parts 


Parts 


Quantity 


Comment 






IT lUd UImWvI \JL IW^SS UdVU 


Lllgliai ICS 


8 trays 


nasic i^miJo 


Vacuum tubes 


Junk bin 


To impress junior engineers 


Transistors 


2 trays 


Plus bin of power transistors, 






bipolar and MOSFET 


Diodes 


1 tray 


Plus bin of assorted and power 






types 


Resistors, 5% 


AH values 


Kit 


Resistors, 1% 


5 trays 


Semi-sorted; get a kit if you 






can 


Capacitors, 10% 


2 trays 


All values ceramic 


Capacitors, 1% 


2 trays 


All multiples of 10 plus bin 


Capacitors, 


Same bin 


Keep 'em small; avoid if 


electrolytic 




possible 


Inductors, xfmrs 


Junk bin 


Except 1 tray subminiature 






shielded, multiples of 10 


Zener diodes 


1 tray 


All low-V low-I values; some 






high- V high-I snubbers 


Current-limiting 


1 tray 


All values I can get my 


diodes 




hands on 


Crystals 


1 tray 


Smattering of frequencies; 






mostly low-frequency 






TO-5 cased 


Pots 


1 tray 


TO-5 cased, single and multi- 






turn, good cermet, most values 


Other 


Small quantities 


Low-power SCRs, TO-5 relays. 



LEDs, opto-isolators, net- 
works of matched resistors 
and capacitors, flashbulbs, 
DIP switches, subminiature 
fuses, Sonalerts, "black blob" 
miniature power supplies ±5V, 

±6V,±12V,±15V; aspirin 

Note: Trays arc plastic 1 S-compartment 7" x 1 J " x 2". 



362 



Arthur D. Oeii^aiige 



3. Save old parts in junk bins; clean them out only when the bin 
overflows or the parts become unrecognizable. 

4. Save old bfeadboards in a drawer. If I have ever used a part be- 
fore, it's in there somewhere, 

5. Take advantage of free samples, within reason. 

if It Doesn't Work Jake Two Capacitors and Call Me in 
ttte Morning 

When students bring me circuits that don't work, they are usually sur- 
prised that I am not surprised. With all the little details that need atten- 
tion, which I am not good at, I don't expect a circuit to work the first 
time. In fact, I plan on it. I put in terminals for observing critical points, 
and jumpers for separating stages and opening feedback loops. A circuit 
board always gets a revision, so you can take them out later. Plus, it gives 
you spaces that can be commandeered for those bypass capacitors and 
protection diodes you just found out you needed. 

ASSERTION: 

Circuits don't just fail; they fail in a certain manner, in a certain spot. 

I grill the student: What did it do or not do? Was there an AC signal on 
the output? A DC level? What were the power supply readings? 

Pass the Pease/Ptease 

Bob Pease has written a complete book on troubleshooting.*^ I will 
mention only a few things I have had the misfortune to become ac- 
quainted with. 

The most common problem is that the power supply is wrong, not 
hooked up, or simply not turned on. CMOS will often power up from the 
input signals via the protection diodes and work to a certain extent. Hie 
symptom is that every signal exhibits remnants of every other, since the 
power supply depends on the signals. Check the supply voltages, on the 
card, right at the trouble spot, wiA a voltmeter cmd a 'scope. 

The next most common problem is that the circuit is not wired accord- 
ing to the diagram! Connections and/or parts are wrong or missing alto- 
gether. Do not expect the circuit to work with even one mistake; mother 
nature is unfoi^jiiving. 

When I had checked out the encoder signal generator and power amp 
driver for the magnetic system mentioned earlier, I hooked them together 
and threw the power switch. Red lights flashed on the power supply. I had 
visiiMS of exotic nonlinear oscillations resulting from the high-powered 
output signal getting back to the sensitive crystal oscillator, and how I 
was going to apply my superior expertise to cure them. The problem? 
In my jerry-rigged satup the power supply leads bad gotten simshed to- 
gether, and the insulation eventually gave up. (Teflon creeps badly with 



363 



Armlog D^grv-Thought Process, Bag of Tricks, Trial and Error, or Dumb Luck? 



time.) I felt rather sheepish when I separated them and everything 
worked. 

And the list goes on. 90% of the time the problem is a stupid mistake. 
Assume you have made one. But, oh-oh, I just said a dirty word. 

Assumptions 

EXPERIENCE: 

Assumption is the mother of [unprintable]. 

The first rule on making assumptions is: Don't. Find out for sure if you 
can. If you can't, proceed, never forgetting that your work is based on 
something that may be wrong. If things just aren't working out, it may be 
that the assumption you made is invalid. While your circuit is doing m&i- 
ing is a good time to review your assumptions, and also your 

Approximations 

Approximations are the lifeblood of engineering, but they can also be the 
death of a system. As above, Don't, unless you have to. ^34 is a cute ap- 
proximation for pi, but punching a button on any scientific calculator will 
get you the actual value to a disgusting number of decimal places. Pi = 3 
is a poor approximation, for enjergency use only. However, should you 
get into trouble using it, the appendixes give proofs that pi = 2 and pi = 4. 
Pi = 3 may be obtained by averaging the two proofs. This will distract 
your supervisor long enough to forget about writing up your deficiency 
report. These proofs should also teach you two valuable lessons: 

1 . Don't believe everything you read. 

2. Don't deal with disreputable persons. 

When you do have to approximate, keep the fact not too far down in 
your memory. Are the approximations cumulative— piling up on you? 
There is a tendency to make an approximation that is in itself reasonable, 
but then to proceed as if it was absolute truth. 

In my PhD thesis I calculated the signal and noise frequency spectra 
based on the best models I could come up with, and derived the optimum 
filter. It came out a very narrow spike, infinitely steep on the upper side. 
I traced the causes to an approximation X had made in the noise crfcu- 
lation to make the math doable, which made the noise spectrum fall off 
extremely rapidly with increasing frequency; and an assumption about the 
target that gave a spectrum less steep, but with a precisely defined maxi- 
mum frequency. If the real target spectrum was actually a Httie bit lower 
than I had estimated, the "optimum" filter would miss it completely. I 
settled for a flat-topped bandpass, which worked fairly well. It did pay to 
make the lower cutoff as steep as practical, as the noise spectrum was 
indeed quite steep (but not as steep as my model indicated); keep die 
cutoff frequency as low as possible without admitting a horrendous 
amount of noise; and settle for what signal was left in the resulting pass- 
band. The inaccurate analysis did offer a possibility for improvement — 



364 



Arthof D. Etelagrar^ 



rather than try to make the model more accurate to reflect the poorer re- 
sults, try to alter the system to be more like the original inaccurate model 
and actually achieve the optimistic results! 

Ground: As Solid as the San Andreas Fault 

Here is everybody's favorite approximation. Ground is one of the most 
useftil concepts we have, but it is only a concept. You can define one in- 
finitesimal point on the card as zero voltage, but all others are at least 
slightly different, possibly seriously different. Entire chapters have been 
written on grounding; probably books. Suffice it to say that there are two 
popular methods, which paradoxically are virtually opposite! One is to 
use only the one point as ground. Each circuit must have its own individ- 
ual ground lead to that point so ground current from no circuit flows in 
the ground lead of any ottier, inducing an undesirable voltage. This is 
generally impractical, but useful in some special cases. This is the idea 
behind "sense" leads on a power supply, "four-terminal" measurements 
on an impedance bridge, and separate analog and digital grounds. 

I prefer the brute-force approach — ^the ground plane. One side of my 
cards will be near-solid copper. Power supply buses may be integrated; a 
well-bypassed supply looks like ground to AC signals. Short leads may be 
integrated; long leads should be run around the edge. A copper sheet is 
about as low an impedance as you can get, at least at any temperature you 
would care to work in. Plus, there are a number of side benefits. Ground, 
the most common (no pun) connection, only requires a feedthrough. 
Le^s mostly have capacitance to ground rather than to each other, the 
latter generally being harder to deal with. The cards are basically self- 
shielding; electromagnetic interference isn't going to get any further 
than the surface of the next card. 

Clean Thoughts 

Just as two adjacent leads on a circuit board make a dandy capacitor, two 
adjacent leads on a dirty circuit board also make a resistor. Even a flux 
that is initially non-conducting may carbonize after repeated overheating, 
and one can make resistors out of carbon. I hereby lay claim to having 
invented the light-emitting circuit board. Also the smoke-emitting circuit 
board. Not a component, mind you, the board itself. I figured the grunge 
accumulating from numerous changes didn't matter because it was from 
power supply to ground, but apparently even that has its limits. 

REMEMBER: 

Smoke is one of the seven warning signs of circuit trouble. 

There is a lot of argument about cleaning boards. They are working on 
new "no-clean" fluxes. I hope they work better than the old ones. I built 
a Heathkit depth finder which had specific instructions not to clean the 
board, which I thought rather optimistic for electronics that had to operate 
in saitw^er atmosphere. It worked for a day and a half. I took it apmt and 



m 



Anatog Design— Thought Process, Bag of Tricks, Trial and Error, or Dumb Lucl(? 



cleaned the board. It then worked until something mechanical failed years 
later. 

There is a possibility of solvents leaching contaminants into non- 
hermetically-sealed packages, such as epoxy DIPs. I have never expe- 
rienced this, but I do not submerge the cards, just brush/spray them 
off. I have experienced the problem with switches and pots, even the 
**se^ed" types. Keep fluids away from them, or add them after cleaning. 

My personal favorite cleaning method is acetone followed by ethyl 
alcohol In spite of the dire warnings on the label, acetone is pretty in- 
nocuous. At the dispensary (that's Navy talk for first-aid station) they 
clean adhesive tape goo off with acetone. And if things are going 
really badly, you can drink the alcohol instead of wasting it on the 
board. 

Covering a mess with plastic spray doesn't get you off the hook. Water 
molecules do get through plastic coatings. If the board is clean, it will be 
distilled water and probably not hurt; but if it is dirty, you just get 
plastic-coated slime. 

Instrumentation— Your Electronic Eyes 

Of utmost importance in troubleshooting is proper test equipment. TBible 
20-4 gives a list of items I would not want to be without- Herewith some 
further comments: a friend of mine was actually told he could have only 
one piece of test equipment. (He quit.) If I had only one choice, it would 
be a high-speed variable-persistence (memory) analog 'scope. It is your 
best shot at seeing what's really going on. Digital 'scopes have some ex- 
cellent features, but keep in mind that you are only seemg a processed 
version of part of what happened some time ago. If there is any doubt, 
connect both analog and digital 'scopes to the point in que^ipn, tfiey 
don't agree, at least one is lying. If the trace on one changes si^ificantly 



Table 2(M Stock of Equipment 



Instrument/Equipment 


Comment 


Analog 'scopes 


#1 measuring instrument; fast variable-persistence 




is best 


Digital 'scope 


Pretty pictures, but rely on #1 


Spectmm analyzer 


Mine does filter responses in one sweep — nice 


Printer/plotter 


If it's digital, it should give you a printout 


Voltmeter, DC, digital 


Good accuracy, but remember, it's an average 


Voltmeter, AC, true-RMS 


Digital plus analog meter, which is great 


Function generators 


AM, FM, sweep, noise, pulse, synthesized, 




variable-phase 


Filters 


Butterworth, Bessel, Elliptic 


Counter/timer, LCR meter 


See text 


Attenuator box 


IdB calibrated steps; stop fiddling with pots 


Power supplies 


Constant-current and regular 


Temperature chamber 


See text 


Microscope, binocular 


Amazing, the crud you see with 8x magnification 


Calculator, scientific 


Cheap 


Slide rule 


Backup for above 



366 



Arthur D. Detagrange 



when the other is disconnected, it was influencing the circuit unduly. I 
had a circuit that appeared to have a low-level 25KHz oscillation; it dis- 
appeared when I mmd off the digitri *scope. If you have a glitch that 
appears at the beginning of the sweep on an analog 'scope no matter 
what point you probe, suspect that it belongs to the 'scope. 

A spectrum analyzer is handy for a lot of jobs» but know that it does 
not really compute a Fourier trmsform, or even a FFT, but a DDFT — a 
Doubly Discrete Fourier Transform, which has some limitations. Digital 
meters give you so much apparent accuracy they can be misleading. They 
can define only one parameter, and have to average that one. Is a LOOOV 
DC signal n^aiingfiil if it has IV AC noise on it? 

AXIOM: 

The neater the display, the more likely it is hiding something. 

I like synthesized function generators, with dial option if possible. I 
know the frequency is right where I set it. I have four, and have trouble 
keeping one in the office. Pulse generators should have variable rise and 
fall tin^s to reproduce the real signal accurately. Laboratory filters are 
indispensable; again, I keep both continuously variable and precisely 
settable. Any old-timer who had to fiddle with an impedance bridge ap- 
preciates modem LCR meters. Read the manual, which should point out 
that it is simply a tool using a particular method to determine a parameter 
which is only a definition. Mine will measure inductors two ways, and the 
numbers are usually quite different. Parts do get damaged, or even misla- 
beled, once in a while. A capacitor labeled "100" can be either lOOpf or 
10 (followed by "0" zeros). Also, the only thing you can be sure of about 
a 0.01 -microfarad capacitor is that it is not exactly 0.01 microfarad, or at 
least not for long. Put some heat on it and watch it change. Which brings 
up the most controversial item: 

I keep a small temperature chamber right in my office, and do not con- 
sider a prototype circuit design finished until I have used it. Temperature 
is generally tte best way to test the sensitivity of your new circuit. If you 
don't do it, mother nature or the air conditioning man is going to do it for 
you. Spray-freeze and soldering iron tips are good for isolating an offend- 
ing part, but too crude for anything else. After all, most parts will fail if 
you melt them. If nothing else, put your circuits in the refrigerator, bring 
in your blow drier (or your wife's if you have no hair left). Here on the 
East Coast, where the temperature is usually disagreeable, I used to hang 
circuits out tfie window. 

All the equipment in my room adds up to less than half of my yearly 
salary plus overhead. Do try to explain to management that good equip- 
ment will more than pay for itself by increasing your productivity, and I 
hope you have better luck than I did. When I finally got a spectrum ana- 
lyzer after years on a project, I took one look at the system output and 
threw away all my test data. The inductance of a transformer winding was 
resonating with a coupling capacitor, and my spectmm that should have 
been flat had a huge hump in it. Of course, had I suspected I would have 



367 



Analog Design— Thought Process, Bag of Tricks Jrial and Error, or Dumb Lucl(? 



borrowed an instrument or checked it another way, but that's the point: 
without the analyzer I never suspected. 

Classic case of false economy: In developing a system, the one poten- 
tial problem we were unable to check was hermetically sealing the special 
hybrid package. Management wouldn't approve the purchase of a $10,000 
sealing machine. Guess what gave us the most trouble, being the last prob- 
lem solved before successful production^ — ^achieving a herm^c seal. The 
hidden costs of the delays involved are hard to quantify, but I figure it cost 
us over a million. 

On Disproving the Laws of Physics 

True story: I designed a system that worked from a battery, 28V @ 
50mA. Years later we wanted to adapt it to another system whose battery 
was 14V @ 2.5mA, a voltage reduction of half arid a current reduction of 
20. (The battery was special, and hence a given; a last resort was twin 
batteries,) I thought I could do it with minor improvements rather than a 
complete redesign. Not redesigning would have several advantages: a lot 
of retesting would not be necessary; we could be sure it would fit in the 
special hybrid packages; the layouts could be reused, at least as a "mule" 
for demonstration. New low-power op amps, comparators, and voltage 
regulators had become available in the decade and a half it took DOD to 
get the original system into production, which were of some help. 

PREDICTION: 

If an ideal op amp is ever produced^ it will inexplicably he unavailable 

in a quad. 

I went through each separate circuit, looking at every part, to minimize 
power drain. I discarded two of the three regulators, reducing current drain 
and saving voltage headroom. Some adverse interactions occurred, but 
were cured with better design and lots of capacitance here and there (my 
mythical aerosol can of "spray capacitance"), neither of which cost cur- 
rent. A lot of impedances were unnecessarily low. Savings snowballed; a 
lower-power circuit had a lower input current, which could use a larger 
biasing resistor, which put less load on the previous stage, which could 
then be lower power, etc. I thought I had it solved, but had some discrete 
boards made to be sure. The first board exceeded 2.5mA considerably. I 
rechecked it section by section. I made another board, which was no better. 
Finally I realized the system required significantly more current than the 
sum of its parts! That pointed to an interface problem, and I soon found it. 

The oscillator (the one mentioned earlier that needed stray capacitance) 
worked fine, but the rise time was slow. It was driving CMOS, which 
draws no current in either digital state, but a lot in the time spent in the 
Unear region in between. The obvious solution: insert a Schmitt trigger 
The not-so-obvious non-solution: prefab Schniitt triggers don't do the job. 
The input impedance is infinite and the output switches cleanly, but some- 
thing in between is still conducting. I devised my own (Figure 20-8) out of 
the only CMOS logic circuit I could find where I could get at the individ- 



388 




Rgum 2G-8. 
"Nocurrenf 
Schmitt trigger. 



OUT 



CP HOP 7 (^XCBPT KBSl^TOn) 

ml transistors, the 4007, and one resistor. The output inverter is unfortu- 
nately hard-wired between the supplies, and the resistance must be chosen 
according to the frequency, but it fixed the problem. Adding an IC is easier 
in a hybrid than a circuit board; the resistor chip was as big as the IC! 

The new circuit did introduce another problem. It switched close to the 
rails, and the op amp driving it only got within about a volt of the rails. 
This was fixed by adding forward diodes in series with the power supply 
and ground, effectively reducing the supply voltage of the 4007. There 
was still plenty of ou^ut swing to drive the rest of the CMOS. 

H«rirt9 Achieved True Failure 

OK, so now you've checked everything, and your circuit definitely is not 
going to work. Don't give up just yet. (There's always tomorrow.) Is 
there some spot where you approached something the wrong way, maybe 
even backwards? My first version of the filter of Figure 20-2 failed, 

369 



AiHiidg Desi^v-Thought Process, Bag of Tricks Jrial and Error, or Dumb Luck? 



before I even tried it! When I first found a circuit that gave the desired 
transfer function, I was in a hotel room (on travel). I was redrawing my 
magnificent invention neatly, which I normally wouldn't do till later, 
when I realized it was not DC stable. Aarrgh! How could it do this to me? 
And I had a sinking feeling that if I could fix that, it would then be unsta- 
ble at high frequency. But wait a minute — it already was! That rang a bell 
somewhere between my ears. I went back to work on it, and sure enough, 
swapping the ends of the Wein bridge (to the form of Figure 20-2) fixed 
both problems. Can some alteration fix the problem without destroying 
the purpose? FM radio didn't work until they realized it took more band- 
width than simply the bandwidth of the input signal or the frequency 
deviation. In fact, FM takes 10 times the bandwidth of AM, necessitating 
higher radio frequencies (RF), but it's worth it. On the other hand, it still 
doesn't work in theory — the theoretical bandwidth is infinite. But lop- 
ping off a little bit of power at the higher frequencies doesn't hurt appre- 
ciably, which shouldn't surprise an engineer. 

Failure should just point you in a different direction. This is an iterative 
process which will often get you to something workable. If you wind up 
where you started, look for some point to break out of the circle. 

It doesn't happen very often, but the circuit, or at least part of it, may 
do something useful other than what you planned. The circuit I spoke of 
earlier that performed the wrong function correctly could have been use- 
ful in another system. It never was, but I figure about half my oddball 
ideas eventually found use. 

Lastly, be able to recognize real dead ends. There are theorems iiat say 
certain things can't be done; e.g., Nyquist and Shannon. Before Shannon, 
there was widespread opinion in the Navy that any signal detection prob- 
lem could be solved with enough effort. Not so. I've never gotten an 
award for it, but some of my proudest achievements have been when I 
was able to stop a project that wouldn't have worked, and saved the tax- 
payers a bunch of money. 

If it can't be done, what is the nearest thing you can do, and is it use- 
ful? When the Ground-Fault Interrupter (GFI) first appeared, I couldn't 
figure out how something electromechanical could open the circuit fast 
enough to prevent electrocution. The answer is, it can't, if you provide the 
initial path to ground. It instead hopes to detect a prior leakage to ground 
and open the circuit before you touch something that should be ground 
but has become electrified. It's a lot better than nothing! 

Failure Analysis 

Don't automatically throw deceased parts in the trash can. Failure analy- 
sis laboratories can do some amazing detective work. There is always a 
slight chance the problem is not your fault! When power MOSFETS be- 
came available, we had a rash of failures, even though we were not ex- 
ceeding the ratings. Our Failure Analysis Lab detected something going 
wrong in the substrate, and found a publication detailing the problem. 
The inherent reverse diode was actually part of a transistor which self- 
destructed at high current. The manufacturer cured the problem, but the 

370 



Arthur D. Ddagratige 



part number didn't change; one had to look at the date code. Note: It is 
very difficult to remove an epoxy case without destroying the device it- 
self. You may have to use units in a ceramic package or metal can just so 
the lab can get them apart. 

Look, Mom, No Smoke! 

Now your system (apparently) works. The next step and the one follow- 
ing are important, but one or both often get neglected or omitted entirely 
in the rush of things. In the Gov it's the end of the fiscal year when the 
money expires; in industry I gather it's the time-to-market goal. 

How well does it work? Sure» it meets the specs, but that's not the 
whole story. I like to say, "Play wi± it." That turns some people off; 
rephrase it if you like. What I mean is exercise it, use it, misuse it, abuse 
it, duplicate it (even if you only need one). A lot of bad results can show 
up, and better you find them tiian someone else. 

1 . It csm -t be reproduced. 

2. It only works sometimes. 

3. It works for a while, then quits. 

4. It exhibits peculiarities under certain conditions. 

5. It fails when the temperature or supply voltage varies. 

Believe bad-looking data points, unless you have a very good reason 
not to. I had a circuit that worked, but required more battery voltage than 
I thought it should. I checked voltage drops, and found momentary peaks 
of 4V (no decimal point) across a Schottky diode, which I had used to 
minimize voltage drop!, paralleled it with an ordmary silicon diode, and 
gained 3V on the allowable battery voltage range. Why not just use a 
heftier Schottky? Reverse leakage was a problem. 

Another time I was plc^g a filter response which looked OK, but I 
noticed the amplitude was way down. In reaching around to the back of 
the signal analyzer, I had connected to "Source Sync" rather than "Source 
Out"! The former was a short pulse, having a flat spectrum like the ex- 
pected pseudo-noise, and naturally in sync with it. The result was correct 
in this case, but in turning the drive amplitude all the way up to get more 
output, I could have overloaded the circuit. Just looking at the output may 
not be good enough, due to the "hidden node" problem. This most com- 
monly occurs in multi-stage low-pass or bandpass filters. The output 
looks clean, but back along the line some stage is overloading. (I call this 
"going digital.") You will get signals showing up in parts of the spectrum 
where they don't belong. I put the highest-Q (peafciest) stage last. It is the 
most likely to overload, and I should see it. The problem is particularly 
insidious in filters like that of Figure 20-5, where some op amps are not 
in-line, but off to the side. Check every op amp output and input to be 
sure its range is not being exceeded. 

Don't assume it will get better in production; it usually goes the 
other way. 

371 



Artatog Desigiv-Thought Process, Bag of Tricks, Trial and Error, or Dumb Luck? 



RULE: 

If it only happens once, it might be a mirage. If it happens twice, 

it's real. 

Intermittent failures are the nastiest to locate. First, duplicate the con- 
ditions under which it happened exactly, including variables you don't 
think should matter. I can cite instances where the time of day had an 
effect. If duplicating conditions doesn't cause the problem to reappear, 
start varying things, everything. The circuit may be marginal with respect 
to some parameter. 

THEOREM: 

Zero is the reciprocal of infinity. Infinity does not exist; therefore 
neither does zero. 

This has some practical ramifications: in our world a voltage typically 
decays exponentially. After a few time constants it's pretty far down, but 
it is not zero. If you started with lOkV, you better wait a lot of time con- 
stants, or you may get some do-it yourself shock therapy. Secondly, once 
you get below about half a volt, semiconductor junctions cease to conduct 
and capacitors may stop discharging, especially electrolytics, which have 
a tendency to recharge some all by their lonesome. One result is a circuit 
which always works right the first time it is turned on, but sporadically if 
power is turned on and off. It may be getting preset into a wrong state, 
requiring some bleed resistors across capacitors. 

A related problem is that we usually trust to luck what happens when 
the power is turned on or off. That is, until we experience an unignorable 
number of failures. If a circuit works once or twice and tiien fails, the 
problem may be large capacitors charging or discharging into a sensitive 
node. Most recent devices will tolerate rail-to-rail swings, but observe that 
with the power turned off that is zero volts! Connecting low-impedance 
sources with the power supply turned off can damage ICs, even those with 
protection diodes. 

I have seen so many "impossible" occurrences I long ago lost count. 
Once we had a receiver apparently trigger on the wrong code, a serious 
problem, one that "couldn't" happen. We kept pinging, and after awhile 
it happened again. We tried some other codes with no problem, then re- 
turned to the original code, and it happened again. We finally realized it 
only happened when tte receiver had an "8" in the code where the trans- 
mitter was (allegedly) transmitting a "9," and then only sometimes. It 
turned out the shipboard generator wasn't quite up to the task. The line 
voltage would drop below the spec on the power supply during transmit, 
its output would drop out of regulation, the VCO could not achieve its 
maximum frequency, and the transmitted signal was somewhere in be- 
tween an "8" and a "9"! It was fortunately a temporary generator and the 
problem was solved by taking some other equipment off the line, but we 



372 



Arthur D. Detegrange 



did add a note to the operating procedures to make sure the line voltage 

was up to par: 

Be aware erf three realities which are similar, but different: 

L What you want to see. 

2. What you actually see. 

3. What is actually there. 

Try to keep toward the bottom of the list. 

Increasingly I get failures in devices I have purchased^ look closely at 
them, and spot an obvious flaw that would have been caught in a reason- 
able testing program. Testing is expensive, so do it as efficiently as you 
can, but don't skip it. Also, be aware that we engineers have an inherent 
problem with testing in that we naturally handle our products with re- 
spect, not abuse. Loan it to a college student; send it through the U.S. 
nfiail. 

HERESY #1: 

I do not use BSD protection when breadboarding. 

If 1 am designing a part that is sensitive, I want to know it as soon as 
possible. Actually, in 50-yearold buildings in the Washington, DC climate 
I have never had a problem show up. Production? Different story. I use as 
much protection as possible for equipment going out to a customer. I may 
or may not run BSD tests on the product, depending on the application. 
M^jy of my devices don't get handled after assembly. 

CONUNDRUM: 

Is a good device useful if it can't be tested to show that it is 
indeed good? 

The military generally says no, but there are obvious exceptions. Very 
limited testing can be done on explosive devices. I am sure Chrysler 
doesn't test each air bag. NASA cannot completely duplicate the lunar 
environment. 

HERESY #2: 

I have a dislike for self-test indicators. 

It's a great idea, but they often inspire false confidence. Many don't 
check much more than the battery. Often it's impossible. The only way to 
really test a smoke detector is with smoke. Pushing the button tells you 
the battery can sound the buzzer, which is nice, but it should be labeled 
"battery test." 

A particular problem I deal with continually is this: a fuse (electrical 
type; the ones that set off explosives are spelled "fuze'*) makes a dandy 
compact, inexpensive, one-bit, non- volatile write-once one-way memory 



373 



Analog Design— Thought Process, Bag of Tricks, Trial and Error, or Dumb Luck? 

(WOOWM?). It is great for "sterilizing" explosive devices, performing 
basically the same function they do in civilian life. The problem is how to 
test it. The sterilize function must be tested on each unit, somehow; this is 
a requirement for all safety features. To do this without actually blowinf 
the ftise and dudding the device, we test the cards using a "constant- 
current" power supply. These limit at a precise current; set it below the 
fuse rating and it will not blow. (Most fuses blow around 100% 
overload — twice the rating.) Note: An ordinary "current-limiting" power 
supply will not do. It limits only after the monster output capacitors have 
discharged, by which time your fuse is probably blown, or worse yet, 
dairiaged. For the same reason you have to be careful about how much 
capacitance is in the circuit. 

Two additional cautions: The material inside the fuse is very similar 
to the solder you are using on the outside. Overheat it and you change 
its electrical and/or mechanical properties. Also, since it takes a certain 
amount of power to melt the fuse, the low-valued ones can require as 
much as 8V across them to blow. They are not meant for 5V supply 
circuits! 

I like constant-current power supplies for testing ordinary circuits, too. 
If you make a mistake, they are far less likely to damage parts. Also, you 
find out exactly how much capacitance you need on the power supply 
bus. A marginal circuit may work on an ordinary power supply, woric on a 
fresh battery, then fail as the battery discharges and its internal resistance 
goes up. Turn the current setting down until the voltage starts to drop. 
Does the system oscillate or latch up? l\im it off and on and see whether 
the system will power up on a marginal battery. I use the Hewlett-Packard 
6177 constant-current power supply. Keithley also makes some. I have 
four, and they are often all out on loan. In an emergency you can usually 
fake it using a constant-current diode, which is another device I use a lot. 

One Last Look 

Stand back from your design and evaluate it objectively, as if it were 
someone else's. What did you set out to do? How did the objectives 
change along the way? Is there now anything that needs reevaluating? 
It is embarrassing to have someone point out parts that are no longer 
needed, and it's happened to me. Can that which you have accomplished 
be applied to something else? Or extended further to create something 
new? Half my patents were side issues, "bootlegged" off my assigned 
work. 

The Job% Not Over Tiirt^^ 

Engineers are often so enraptured with their creations they don't bother to 
advertise. I speak as a guilty party. 



374 



Arthur D. Del^mge 



OBSERVATION: 

If you build a better mousetrap, the world may beat a path to your 
door^ but it will be to demand a contribution for faflierless mice. 

At the very least, document your work to the extent that someone else 
can figure it ml if you lose an argun^nt with a semi on the way home. If 
you have trouble writing it down, do you really understand it? 

HERESY #3: 

I do not write everything down in bound notebooks (or computers). 

80-90% of my ideas are worthless; why let them pile up and make it 
more difficult to find the good ones? On the l^r, I keep the first sketch 
(for patent purposes), the most recent (for obvious reasons), and just 
enough in between so I can retrace the evolution of a design if necessary. 

I use a vertical, time-dependent filing system, otherwise known as 
letting it pile up. How long ago I referred to it determines how deep it is 
in the pile. If the pile gets too deep, it will avalanche of its own accord. 
Then I sort it: unnecessary and outdated stuff (most of it) into the trash; 
important stuff into loose-leaf notebooks and a couple of alphabetical 
files. 

probij:m#1: 

Books niust be put on a shelf. llTey make the pile grow too fast, 
and they hurt when they land on you. 



PROBLEM #2: 

For a while I was afraid to touch the pile because occasional noises 
indicated something was living under it. 

I also use a secondary filing system for administrivia: I paper my walls 
with organization charts, purchase requests, time sheets, etc. I have re- 
ceived complaints that this made the room uglier, but that is a weak argu- 
ment for steel walls painted battleship gray. 

BiWiretfieftoatiifks 

When documentation becomes an end unto itself, it becomes self- 
defeating. The following people will be among the last to board the 
lifeboat if I am in charge: 

People who are more concerned with how pretty the diagram looks 
than wtetfier it is understandable. In the past few months I have wasted 
time both because: (1) a dot on a four- way connection was almost invisi- 
ble on the Xerox and the leads didn't get connected, and (2) where there 
was only a crossover with no dot, the leads got connected anyway. If 



375 



Artiriog Desigii— Thought Process, Bag of Tricks Jrial and Error, or Dumb Luck? 

there is any doubt, I put a hump in a crossover and use only "tee" connec- 
tions plus dots anyway. 

Drafting types have no appreciation of how a circuit works; they can't 
be expected to. Don't allow them to show the input resistor next to the 
output with lines running clear across the page because there was a little 
more room there. The circuit has to be arranged logically; the diagram 
should be arranged similarly. It recently took me a long time to figure out 
a diagram for a simple system, which was particularly aggravating be- 
cause I had designed it. The lines to a resistor crossed, like it was twisted. 
Another lead crossed itself; it did a loop-the-loop. Computer drafting 
seems to have made this worse, but I'm not sure why. Insist on good 
drafting. A few people can see how a circuit works no matter how badly 
it's drawn, but most of us need all the help we can get. 

I had seen a particuhu* narrowband filter circuit in severe books, but 
it didn't appeal to me. In fact, it wasn't obvious to me how it worked. 
Eventually I got around to analyzing it and found out it was a circuit I was 
already using! I draw it as shown in Figure 20-9. If you are used to the 
other way, you may not recognize this one. I prefer this way because I 
think it makes what is going on more obvious, at least if you are familiar 
with the properties of the bridged-tee. The circuit has unity gain at reso- 
nance only by virtue of the input being brought in through a large resis- 
tance to a low-impedance point. (Observe the note that the circuit is 
intended for high-Q applications,) The true circuit gain as far as the op 
amp is concerned is greats than Q squared! I was getting poor perfor- 
mance using a 741 and didn't understand why until I appreciated this fact. 
7.5KHz and a Q of 50 might sound like 741 stuff, md separately could 
be, but here it means I needed a gain-bandwidth significantly greater than 
35MHz! I got noticeable error with the fastest op amp I had. The op amp 
still has to be unity-gain compensated because at high frequency (where 
oscillations will occur) the circuit has 100% feedback. These properties 
were not obvious to me with the circuit drawn the other way. 

Similarly, layout personnel are going to simplify their job, not yours. 

OBSEIWATION: 
If there are two leads on a board, the layout person will want a 
two-layer board. 

Insist on a ground-plane board for serious analog work. One of the 
times my request was ignored the board proved absolutely hc^less. Wfe 
had to scrap it and start all over. The opposite may happen if the drafting 
room needs work. I got back a board with three identical channels laid 
out three different ways. So much for matching . . . 

Next is technicians who tie-wrap all the leads together tight as a banjo 
string. One single lead will tighten first, and together with the solid mass 
it makes a high-Q system, and if the system is hit with a vibration at its 
natural frequency, that lead is a goner. Loose leads vibrate individually, 
usually not much, and bang against each other if they do, damping the 



376 



Arthur D.Oeiagrafige 



IN 




Figure 20-9. 

Narrowband filler. 



^ OUT 



BIA/ 



3cib cS?2Trf?c 
for q » I 



oscillations. They also have a lot less coupling capacitance. I once de- 
signed drivers for a high- voltage electroluminescent display which 
worked until all the leads were neatly lashed together. Then when one 
segment lit, they all lit. It was decreed by the powers that be that leaving 
them loose was unacceptable, so I finally had to use ribbon cable with 
every other lead grounded. 

My branch once built a computer, an entire 6-foot rack back then, us- 
ing only black wire. It looked very tidy, but it was nearly impossible 
to trace anything. We almost gave up and rewired it before we got it 
debugged. 

Next come supervisors, the ones who think your desk and lab bench 
siiouU be cleaned off at the end of the day. If I took all the piles on my 
desk, combined them, and squared them up, I would have trouble finding 
anything. But I usually remember which pile I put things in, and if a cor- 
ner of a page is sticking out with section D of an LM339 on it, I know 
what that drawing is. For some reason I can rememb^ that, although I 
never seem to remember that the pin numbers go counterclockwise look- 
ing at the top of a board . . . 

P^cular emphasis for those who **correct" my reports which are al- 
ready correct. Computer spelling checkers and secretaries come to mind. 
My "baseband" signal became ''basement." Once a secretary switched 
something in a way I didn't like, but she was insistent and it wasn't worth 
fighting- Apparently the delay to the next revision was longer th^ her 
memory, because she then switched it back. 



377 



Analog Designs-Thought Process, Bag of TrickSrTrial and Error, or Dumb Luck? 



FLIP-FLOP RULE: 

If you drag your feet long enough, the rules will change baek, 
so arrange for an even number of revisions. Applies to clothing 
fashions, also. 

And then there are the quibblers that insist that "low-pass" must be 
hyphenated but '^bandpass*' cannot be. 

Lastly I must mention my dear sister who nearly gave me heart failure 
at an early age. I was building a Heathkit and she came over to mspect, 
'That doesn't belong there!** she said emphatically, pointing to a resistor I 
was about to solder. I was mortified. My first mistake on a kit, and my kid 
sister had caught it. "Why not?" I asked, furtively glancing at the instruc- 
tions. "Because the colors clash with the one next to it!" came the logical 
answer. 

The Report 

Many engineers hate writing reports, but I enjoy it, mostly. Beginning is 
usually the hardest part, so I don't. What I mean is, I start in the middle, 
the meat of the report. It is simply what I have done, so I just write it 
down. But I consider that merely an outline. Then I go back and fill in 
the gaps and tack on the ends. 

What was the assignment? Who gave it to me? When? Where? (The 
four Ws) I try to forget that I am at the end of the project looking back- 
wanl with hindsight, and go all the way back to the beginning, when I 
first began to think about the project. That is where the reader is. It can be 
difficult for experts to teach because they know the subject reflex ively. 
Remember, you are the expert on this particular thingamabob, possibly 
the only one in the world, because you just invented it! This part cmsti- 
tutes your introduction. 

How did you do it? (The big H) How does it work? How do you know 
it works? Also, what was rejected? What didn't work? Analyze it. (A as in 
Aardvark) This expands the body of the report. 

Then Terminate it. (Gimme a T) By now, if the report is well written, 
the reader has reached the same conclusions you did, but list them any- 
way. Managers often read only the introduction and conclusioB. I had 
one line manager who sent every report back with red marks all over the 
first three pages, but none thereafter. That was obviously all he read. 
This may be why some editors want a summary right at the beginning. 
Conclusions should include recommendations and plans for future work. 
The end may not be the end! Put all the letters together and you get 
W-W-W-W-H-A-T? — which is not a bad description of what the report 
should answer. 

Bureaucracy 

Engineers should not be content with theories about how nice things 
should be, but should apply their talents to making things work in the real 
world. Bureaucracy is part of the real world. Plan on it, just as you would 



378 



Arthur D. Deti^ange 



keep in mind that your system is probably going to have to fit in some 
sort of package. 

Horror story #1 : 1 needed some shielding between the transmitter card, 
which was generating 100 V, and the receiver card, which was detecting 1 
microvolt, a 160dB difference. Not surprising. It was fairly easy: put them 
at opposite ends of the rack, and leave unused card slots adjacent to each, 
insetting empty c^ds. Any old card would do, since I used all ground 
plane cards. What was not easy was convincing the documentation de- 
partment. They could not handle an undefined card. They made up a 
drawing for cutting and drilling a blank piece of board material. This 
shorted all the pins on the connector together, including the power sup- 
plies, which were bussed to every slot. So they relief-drilled all the holes, 
but then the ground plane wasn't connected. They fixed that, but I'm 
sure diat had not ground been the middle pin, some would have gotten 
mounted backwards and failed. I would have saved money in the long run 
by laying out and fabricating a card with nothing on it. Using defunct 
cards would have worked, too, but it did occur to me that every card has 
to have a eofr^^poflding testing spec, and I could envision having to write 
one that said, **T%is card shall not function properly in any of the follow- 
ing ways: . , 

Horror story #2: The same system used only J<W 5% resistors. In one 
spot I needed 3^W, so I simply paralleled two. This was not acceptable to 
the powers that be; I was obviously wasting a resistor. So another spec 
was called out, the parts list changed, and the circuit board redone. Then 
progress stopped half a dozen times while someone located me to ask if 
one callout or one pad spacing was really supposed to be different from 
all the rest. Worse yet, some testing should have been redone since the 
value had changed slightly (for some reason values have been carefully 
arranged so half a s^dard value is almost never another staiKiard value), 
but they were too busy doing the paperwork to notice. 

And then there are those who insist on assigning arbitrary numbers 
instemi of codes. Rev B could have been yesterday or a decade ago; a date 
tells me for sure. The miUtary takes a perfectly readable part number for a 
capacitor which already contains the necessary information and replaces 
it with a meaningless number that you have to look up in a table that no- 
body has. And what does the table tell? It gives the cross-reference to the 
original part number! How to do it right: you may have heard of the "mir- 
acle merrory metal" NiTiNOL. Its name tells you it is an alloy of Nickel 
and Tin and it was developed at the Naval Ordnance Laboratory, so you 
have not only an idea of what's in it, but where to go for information! 
Much better than "Alloy X-IB." 

Fight these bad people. Engineers are usually not argumentative and 
just look for ways arouiKl roadblocks. I think we are the only group other 
than maybe the left-handed Albanian guitar players not protesting for our 
rights. Snarl as you go back to your cage. It keeps them on their toes, and 
may make it a little easier for the next engineer. 



379 



Analog Design—Thought Process, Bag of Tricks, Trial and Error, or Dumb Lucie? 



Intellectual Honesty 

This is not a separate section, nor does it fit into another section. It be- 
longs in all of them. You may at times get ahead by fooling someone 
else, but you will not make much progress fooling yourself. If you have 
read my diatribes before, you know I feel the computer side of our pro- 
fession has at times oversold its product. But we analoggers are not in 
good stone-throwing position, either. Don't make the truth shortage any 
worse; it's bad enough already. Consider how far we have slipped: 

I have several catalogs labeled "digital." There are few digital circuits 
in them; most are binary. I worked with a real digital computer back in 
1957, probably one of the last. It used vacuum tubes, was the size of a 
furnace, and in fact had a stovepipe on it to get the heat out. TTie only 
memory was punched cards, its input and output. 

I have a large number of catalogs labeled "linear." Half the devices in 
them are nonlinear. "Analog" is better, although we seldom^ifl compute 
analogues of anything, other than an occasional inductor. Every "sam- 
ple-and-hold" in my book is really a track-and-hold. "Differential ampli- 
fier" refers to anything from an op amp to a matched pmr of traiisistors; 
the term has become useless. I sent for info on a "hex op amp" in a 
14-pin DIP, an impossibility. I figured they were prewired as followers 
or inverting-only, which might be useful. But it wasn't even that: it was 
six CMOS inverters. I guess "op amp" nieant they wouldn't osdllate 
with feedback, which wasn't too surprising with only 20^^ gam. Most 
zener diodes are really avalanche diodes. 

We talk about voltage and phase, forgetting that both exist only as 
differences. Aii unspecified voltage is presumed to be referenced to 
ground, but what ground? Phase reference is often very obscure, leading 
to a lot of errors, for example in FFT systems. In modulation systems the 
DC component may vanish either because its amplitude is zero or be- 
cause its phase is zero (oops; relative to sine). 

Does it really matter? I'm afraid so. In the next section I will cite a 
downfall from misuse of the term "integrator." One of my favorite gripes: 
op amps have high gmn and wide bandwidth. WRONG. Op amps have 
high gain or wide bandwidth. That is the meaning of gain-bandwidth 
product, inherent in op amps. This carelessness can lead to op amps 
being used where another device would work better. 

Example: A large number of precision full- wave rectifier circuits 
using op amps have been published. Usually frequency response is not 
mentioned. This is a difficult application for an op amp; the frequency 
response can be surprismgly terrible. A sine wave when rectified has sig- 
nificant (^OdB) components out to ten times the fundamental frequency, 
and the time it takes the op amp to slew across diode drops and other 
nonlinearities can be disastrous. There are ways of doing it without op 
amps. One way is to feed the signal to both linear and clipped tnpats of 
a balanced modulator so the signal gets multiplied by its own polarity 
(sneak a look at Figure 20-lOA if you like). The old 796/15% balanced 
modulators were fast, although gain and DC stability were poor 



380 



Arthur D. Dete^ange 




A . WOfiKfV^ eUT TOO <>LaW 



B/A5 




TO Re$ r o f 




(^UT F^T swirci-fes MUST er nuh/ ■spun - so/^f^tY 



Figure2&-10. 

DC-accurate 

Next gripe: Balanced niiodulator circuits having an op amp on the out- baWicerf 
put. Hie modulator output, by definition, is a switching waveform having modtllatofS. 
infinite slopes. An op amp cannot accommod^ these for at least two 
iriterent reasrais — bandwidth and slew rate limits. Although a form of 
low-pass filtering, stew-rate limiting is nonlinear, smd hence generally 

381 



Analdg Design— Thought Process, Bag of IVicks Jrial and Error, or Dumb Luck? 

unacceptable. I needed a balanced modulator where the input signal was 
limited to 20KHz bandwidth, but one-degree phase accuracy was re- 
quired, which implies a bandwidth £rtx)ve a megahertz. Also, better than 
one-millivolt DC stability was necessary. Having a choice between modu- 
lators that were too slow or too inaccurate, I had to devise my own (see 
Figure 20-10). I buffered and inverted the signal with op amps and then 
switched between the two with CMOS switches (Figure 20-1 OB). (Digital 
CMOS transmission gates can transmit analog signals quite nicely, and 
they are fast!) The output impedance was that of the switches, but above 
IMHz the output impedance of the op amps was no better. Note that with 
this arrangement I could put considerable capacitance to ground on the op 
amp outputs since they only had to accommodate 20KHz ( linear), which 
kept their output impedance down at the higher frequencies. It was neces- 
sary to find a trick to prevent the switches from momentarily connecting 
the two op amp outputs together during switching, which drove them 
crazy. The balanced modulator was followed by a low-pass filter, as is 
often the case. Putting its input resistor b^re iht switches (Figure 
20-lOC) prevents the outputs of the op amps from being tied directly 
together if one switch closes before the other opens. (What if one switch 
opens before the other closes? The filter momentarily gets no signal, 
which is a truly minimal glitch, since the signal is in the process of 
switching to its opposite anyway!) Note that the resistance does not dou- 
ble, as only one resistor is connected at a time. 

Important note: If a filter like that of Figure 20-1 A is used, you may 
find surprisingly large switching glitches on the output, exactly what a 
low-pass filter is supposed to get rid of! The path that is supposed to be 
positive feedback becomes positive feed-forward at high frequencies be- 
cause: for fast spikes, the op amp output is allegedly held to zero by (1) 
high loop gain (of which there isn't much at high frequencies) and (2) low 
op amp output impedance (which can be 100 ohms or more, gomg up 
even higher with increasing frequency). Note that the version of Figure 
20-lB is much better because there is a capacitor to ground in the path. 
You can improve the unity-gain circuit by adding a capacitor to ground at 
the output of the op amp, although this n>ay lower the height of the spikes 
by making them wider. The capacitor does nor change the filter character- 
istic as long as the op amp can drive it at any frequency in the passband, 
and does not oscillate. In this case the filter of Figure 20-5 was used. 
Here the inductor blocked the current spikes (Figure 20-lOC). 

Incidentally, I was surprised to find the digital driving circuitry slowing 
my analog circuit down! I found that one side of a 4000-series CMOS 
flip-flop lagged the other by a significant amount; I had to switch to 
high-speed CMOS. This shouldn't have surprised me because a linear 
circuit need only pass the signal frequency accurately, but logic needs 
orders of magnitude more bandwidth. For analog work, a IMHz digital 
switch may not be of any more use at IMHz than an op amp with a GBW 
of IMHz, namely none. 



382 



Arthur D. Delagrange 



Simpli%, Simplify, Simplify 

Simplify as much as possible (but no more)! I have read countless windy 
dialogues which claimed to reveal some new truth but in reality only ob- 
scui5ed an old one. A real classic: 

Years ago I read an article in a magazine where the author claimed that 
by adding an inverting transistor in the loop after an op amp and switch- 
ing the feedback to the noninverting input he had (1) increased the time 
constant of an integrator by a factor of beta, (2) made a noninverting inte- 
grator, (3) achieved a high-input impedance integrator; none of which was 
true. I wrote to the magazine editor, who forwarded my letter to the au- 
thor. I received back a 6-page "proof of his claims. (The circuit only bad 
1 op amp, 1 transistor, 1 capacitor, and 3 or 4 resistors.) I plowed through 
his convoluted analysis. His math was correct; it gave the standard result 
when his complicated answer was simplified properly. Instead, he associ- 
ated somce terms with things "everybody knows" and ignored others. He 
fooled himself and the magazine, but he didn't fool me or the circuit. I 
breadboarded it to be absolutely sure. The author claimed he had tested it 
successfully, but gave no details. 

MURPHY'S LAW, APPLffiD TO OBFUSCATION: 

There may or may not be a simple way of looking at a problem, 
but there is always a complicated way. 

Part of the problem came from the common practice of referring to an 
RC low-pass as an "integrator." It may be technically correct to model an 
integrator as a low-pass filter having a DC gain of 1,{)00,(KX) and a break- 
point of 0.0001 Hz, but it just distracts from the true use. In the old days 
op amps were sometimes described as having an inverting gain and a 
ncminverting gam, both with loose tolerances, Om might not have appre- 
ciated that the two were almost perfectly matched, the basis for a lot of 
good circuits. 

I was work supervisor for a thesis student whose analysis of his system 
produced a result we both knew was incorrect, but neither of us could see 
where he had gone wrong. I suggested a simpler analysis, but he was 
determined to find out why his didn't work, which I didn't want to dis- 
courage. His school supervisor found the error: he had canceled a compli- 
cated expression from both sides of an equation. It turned out to be equal 
to zero, so he had unknowingly divided by zero, leaving nonsense. 

Humility 

Most people, particularly engineers, like to think they are in full control 
of the situation at all times. This is not so. A graphic demonstration is a 
Washington, DC ice storm. It's amazing how the world changes when the 
coefficient of friction changes an order of magnitude. We had a particu- 
larly bad one where, after all the cars piled into each other at the local 
intersection, the drivers got out — and all fell down! It was so slick you 



Analog Desigiv-Thought Process, Bag of Tricks Jrial and Error, or Dumb Luck? 

could not walk; some people literally crawled home. Some loons flying 
south (I am speaking of the birds, not the congressmen) iced up and 
crashed into suburbanites' yards! Recalling this scene reminds me how 
close to the ragged edge we really are* 

THOUGHT PROBLEM: 
What would happen if the value of pi suddenly changed? 

I recommend an occasional dose of humility. If you are overconfi- 
dent, it usually happens automatically. True, you need some self- 
confidence to achieve anything, but you are not likely to learn if you 
believe you already know it all. If you need help, recall that before the 
days of transistors, not to mention ICs, the vacuum tube crew had 
'scopes, oscillators, voltmeters, counters, regulated power supplies, ra- 
dios, TVs, radars, sonars, i.e., most everything we have now. True, usu- 
ally not as nice, although many audiophiles are still hanging qnto their 
tube amplifiers. If all the time and money put into semiconduGtors had 
been put into tubes instead, they would probably be pretty good by now. 
We would surely have integrated circuits, and maybe heaterless versions 
and complementary devices! 

I had almost forgotten that as a graduate student I designed an op amp. 
At the time (1962), tubes worked better than transistors. The op amp had 
only 62dB gain, but that was flat to lOKHz, giving it a gain-bandwidth 
close to lOMHz, an order of magnitude better than a 741 . (Did you ever 
see a 741 with a warning label— "USE OF THIS PRODUCT ABOVE 
IKHZ MAY LEAD TO LOSS OF ACCURACY"? It's true!) It would 
tolerate a 40Q0pF load. Settling time to 0.1% of final value was less than 
10 microseconds, including a 40V step, with the 4000pF load. (Output 
current was 100mA.) Other parameters weren't as good as a 741, except 
input impedance, which was reported as infinite. (Infinity was smaller 
back then, perhaps because the universe hadn't expanded as far.) It had a 
true balanced input, but the only use envisioned for the noninverting infHit 
was a handy place to connect the chopper amplifier. How shortsighted! 
Supply current was significantly higher, especially if you count the heater 
current. It covered an entire card, and we won't talk about cost. 

Have we progressed all that far? Well, yes and no. I sometimes miss 
the warm, cheery glow of vacuum tubes on a cold winter's night and the 
thrill of seeing blue lightning bolts inside them when I exceeded the volt- 
age rating. They don't have transistors that glow purple like the old regu- 
lator tubes, or even LEDs for that matter. 

Luck of the Irish and Non-lri$h 

More than once I have improved a circuit by accident. Typical is: moving 
a 'scope probe, and hence its ground lead, and finding out I had too many 
grounds (ground loop) or too few (no ground connection). Or (keying 
the probe on the circuit and seeing oscillations disappear. (The shielded 



384 



Arthur H Oelagtitige 



cable acts as a shield for whatever it falls between.) Or sticking a capaci- 
tor in the wrong hole. (So that's the point that needs more capacitance!) 

Jim Williams tells of getting the answer to a circuit problem by observ- 
ing the monkeys at the zoo. I would have thought that more applicable to 
management, but the point is that ideas seem to be held up in the brain 
until some trigger springs them loose. If you seem to have a block you 
can't get through, try to get around it^ using whatever sources happen 
along, no matter how unlikely, 

I once had a balky circuit card that would always work for me^ but 
never for the person I made it for, which made troubleshooting difficult. 
But it also gave me a clue. The problem was an unconnected CMOS in- 
put. These have such a high impedance they can be switched by static 
fields. One of us was apparently charged positive and the other negative. 
I was lucky it showed up before it got any farther. 

Engineerirtg Ethics 

In the uniformed military, when an accident happens it is, by definition, 
somebody's fault. Somebody has to be responsible, and you don't want to 
be that somebody. This system has its shortcomings, but it works better 
than the civilian government, where nothing is anybody's fault, no one 
has the responsibility, and mistakes happen over and over again. 

UNANSWERED (LEGAL) QUESTION: 

Where does an engineer's responsibility stop? 

I suspect the average engineer would say a widget is just a widget, and 
how it gets used or misused is beyond our responsibility. It may be logi- 
cal, but others say different, and they have been winning some in court. 
Companies have been held responsible for damage their products did, 
even when warnings were ignored or the equipment totally misused. A 
friend of mine faced a million-dollar lawsuit when the plaintiff named the 
private contractor involved, the highway department, which let the con- 
tract which set the rules, and the head of the department, who delegated 
the authority. Design News carries a legal column every issue. Spec sheets 
carry disclaimers on use in life-support equipment. I recently received a 
shipment of capacitors which included a sheet telling me not only not to 
eat them, but what remedies to take if I did! I am not making this up. 

Two good books have recently been published on disasters involving 
engineering. Most were mechanical problems, but several involved 
computers, two concerned electrical power, and one was an effective fail- 
ure of an analog system. Losses and/or lawsuits in most cases involved 
millions of dollars. Many involved injuries or fatalities. 

What would you do if one of your products accidentally hurt some- 
body? I hope you would feel genuinely sorry, but I also hope you would 
not give up your profession. But, first of all, try to prevent it; Design your 
products as if you had to plead your ease to a judge, who can't operate the 



m 



Analog Cfesign— Thought Process, Bag of Tricks Jrial and Error, or Dumb Luck? 

controls on his VCR, against a lawyer, who is out of jail only because she 
is a lawyer. It could happen. 

Go to It! 

Engineers are needed, now more than ever. We old-timers are weeing out 
one by one. Yet I have mixed feelings about encouraging young engineers 
these days. Our paychecks don't reflect our contribution toward the in- 
credible improvement in our standard of living that has been achieved in 
the last century. And we seem to get blamed for everything that goes 
wrong, and indeed for everything we haven't been able to fix yet. The 
best I can offer is the satisfaction of knowing that you have accomplished 
something worth doing, and that's worth more than money. 

Analog is not a curiosity. It is out there, both on its own and helping 
computers interface to the real world, I hope I have helped you in some 
sm^ way in our small comer of the profession. Returning to the question 
posed by the title of this chapter, if I have presented my case well, you 
know the answer is ALL OF THE ABOVE, Use any tool available to you. 
Touch a computer if you have to; just wear rubber gloves (mentally, at 
least). And don't forget, HAVE FUN! 

References 

1. A. Delagrange, "Amplifier Provides 10 to the 15 ohm Input Impedance " Electronics 
(August 22 1966). 

2. A. Delagrange and C.N. Pryor, "Waveform Comparing Phasemeter," U.S. Patent 
4025848 (May 24 1977). 

3. A. Delagrange, "Lock onto Frequency with Frequency-Lock hoo^^r Electronic 
Design Qmcll 1977). 

4. A. Delagrange, "Need a Precise Tone? Synthesize Your Own " £7)^ (October 5 
1980). 

5. M. Damashek, "Shift Register with Feedback Generates White Noise," Electronics 
(May 27 1976). 

6. A. Delagrange, "Simple Circuit Stops Latching," letter to the editor, Electronic 
Design (May 28 1981). 

7. A. Delagrange, "It Could Be the Ideal Filter," Electronic Design (February 16 1976). 

8. A. Delagrange, "An Active Filter Primer, MOD 2," Naval Surf ace Warfare C^ter 
Technical Report (September 1 1987): 87-174, 

9. A. Delagrange, "Op Amp in Active Filter can also Provide Gain " £DA^ (February 5 
1973). 

10. A. Delagrange, "High Speed Electronic An^og Computers Using Low-Gain 
Amplifiers," U.S. Patent 5237526 (August 17 1993). 

1 1 . Bruton and Trelevan, "Active Filter Design using Generalized Impedance 
Converters," EDN (February 5 1 973). 

12. A. Delagrange, "Design Active Elliptic Filters with a 4-Function Calculator,'^ EDN 
(March 3 1982). 



386 



Arthur aDed^fange 

13. A. Deiagrange, "Feedback-Free Amp makes Stable Differentiator," EDN (September 
16 1993). 

1 4. R, Pease, Troubleshooting Analog Circuits, Butterworth-Heinemann { 1 99 1 ) . 

15. Steven Casey, Set Phasers on Stun, Aegean Publishing Co. (1993). 

16. Henry Petroski, To Engineer is Human, Vintage Books (1992). 



387 



Analog D^ign— Thought Process, Bag of Tricks, Trial and Error, or Dumb Ludc? 



Appendix A 
ProofThatPI = 2 

Circumseribe a sphere with an equatorial circle C (see Figure 20~A1). 
Draw a line R from the equator to the pole; this is the radius of the cir- 
cle. Obviously C = 4R. Therefore the diameter is M of the circumference, 
or pi = 2. "No fair!" you will undoubtedly say, "You used spherical 
geometry!" But that is precisely the point. It has been known for half 
a millennium that we live on a sphere; plane geometry is the wrong 
method to use. 




388 



Arthur D. Detagrai^ 



Circumscribe a circle of diameter D with a square (see Figure 20~B1). 
The perimeter of the square is obviously 4D. Now, preserving right an- 
gles, "flip" the comers of the square in until they touch the circle, as indi- 
cated by the dashed line. The perimeter of the new shape is obviously still 
4D, Now, "flip" the eight new comers in (dotted lines). The perimeter is 
still unchanged. Keep **flipping" the comers in until the shape becomes a 
circle. The perimeter, still 4D, becomes the circumference, so pi = 4. 




389 



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Act of Queen Anne, 243 
Addis, John, 135 
AM radios, 17, 18 
Amplifiers 

distributed, 128-29 

vertical, 135 

wideband. 137-38 
Analog breadboarding, 1 03-19 
Analog circuit engineers in Japan, 35-37 
Analog design, see also Design philosophy 

at home, 200 

and CAD (computer aided design), 

32-^35 

and engineering ethics, 385-86 

facts to know, 263-67 

for fun and profit, 197-218 

and having humility, 383-84 

and inteU^tual honesty, 380-82 

and luck of the Irish, 384-85 

Murphy's Law, 383 

and paperwork, 374-79 
bureaucracy, 378-79 
neatmks, 375-78 
reports, 378 

productivity, 31-39 

requirements, 199 
Analog design, using, 343-89 

defining goals, 346-48 

fijn aspects, 344 

look at problem differently, 349 

working with scientific principles, 
349-52 
Analog designers 

becoming, 41-54 

learning about, 42-44 

survival as, 48-49 

what to read, 47 
Analog Devices, 28 1 
Analog Devices AD606, 292, 293 
Analog Devices AD607, 293, 294 
Analog Devices AD640, 292, 293 
Analog-to digital converters (ADGs), 252-53 



Analysis and Design of Analog Integrated 

Circuits, 47 
Andrews, Gene, 138 
Apple Computer, 140 
Application notes, 47 
Application-specific integrated circuits 

(ASICs), 290-91, 293 
Apprendceships, 1 1 
Art of Electronics, The, 47 
Asiraov, Isaac, 324 
Attenuators, 77-83 
Attitude changes, 21 

Babbage, Charles, 316-17 
Backhghts 
defined, 140 

Hquid crystal display (LCD), 1 39-75 
Barker, Joel Arthur, 310, 314 
Battjes, Cari, 63, 121-38 
Bell, Alexander Graham, 348 
Belleville, Logan, 128, 138 
Bessel filters, 265 
Board of Longitude, 235-48 
Bode analysis, 338-39 
Bono, Edward de, 284 
Bootstrapped source follower, 73, 74 
Bootstrapping the drain, 72 
Bradley, James, 243 
Breadboarding, analog 

capacitances, 105-7 

decoupling, 11 1-13 

grounds, 109-11 

inductors, 107-9 

noise sources, 1 18 

power supplies, 118 

practical, 1 14-17 

principles, 113-14 

resistances, 104-5 
Breadboards, 359-61 

analog, 103-19 

professional, 28 



Brokaw, Paul, 292 
Brown, Julie, 101 
Brown, Lloyd, 233-48 
Bryant, James M., 63, 103-19 

CAD (computer aided design), 32-35 
Calorimetric correlations, 181-83 
Capacitances, 105-7, 132 
Capacitors, super, 356 
Careers, preparation, 17-29 
Cargo cult science, 55-61 
Cathode ray tubes (CRTs), 125 

distributed deflection for, 131 

Tektronix circuits, 149 
Cauer filters, 265 
Chart recorders, 274 
Cherry, Colin, 316 

Chips, see also Integrated circuits (ICs) 
master, 99 
mono 

Chronometers, 233-48 
Circuits 

analog design, 263-67 

video faders, 89-94 
Clarke, Arthur C, 303,324 
CMOS, 254, 266 

Cold cathode fluorescent lamps (CCFLs), 
153, 154-62 

and circuit efficiencies, 192 

complex transducers, 154 

load characteristics, 156-57 

power supply circuits, 157-62 
Communication 

case histories of products, 292-95 

statistical theory of, 286 
Companion, voice of, 326 
Compensated voltage divider, 77 
Computer Applications Journal, The, 47 
Computers 

and innovation, 286 

simulations, 253-54 

tools or companions, 321-26 

voices of, 326 
Converters, impedance, 69-77 
Conviction, voice of, 320 
Counts, Lew, 288 
Courage, voice of, 295 
Crafts, development, 1 1 
Creative moment, 284 
Creeping featurism, 203 
Crosby, Phil, 138 
Cross-unders, 98 
Crystal Semiconductor, 258 
Crystal sets, 280 



Current feedback, 96 

Customer voices, 203, 290-92. 294. 306--7 



Decoupling, 1 1 1-13 
Delagrange, Arthur D., 249, 343-89 
Department of Defense (DOD), 343 
Design, see also Analog design; Analog 

designers 
Design News, 385 
Design philosophy, 330-4^2 
analysis of small pieces, 337^38 
asking computers the right questions, 
336^1 

beware of Bode analysis, 338-39 

and bum-in circuits, 335-36 

checking nature's limits, 332 

Gordian knots, 333-34 

input and output and expected ranges, 
340-41 

and LVceo, 341-42 

making universal chips, 334 

questioning unexpected residts, 330-32 

testing robustness, 339-40 

transient testing, 339 

transistor base currents and incipient 
saturation, 340 

using pieces more than once, 334-35 

when nothing makes any sense, 3 32-33 
Designs 

mask, 98-99 

science or art?, 312-15 
Diddle boxes, 274-75 
Digby, Sir Kenelm, 233 
Diodes 

PIN, 82 

step recovery, 267 

super, 93 
Distributed amplifiers, 128-29 
Ditton, Humphrey, 233, 234 
Dobkin, Bob, 140, 288 
Donovan, Paul, 142, 145 
Double-pole double-throw (DPDT) relays, 
79 



Edison, Thomas Alva, 295-97, 299, 300, 
304 

Einstein, Albert, 304 
Elantec (company), 10 
Electrical Manufacturing , 148 
Electronic construction, 25-26 
Electronic Design, 2i2>\ 
Electronic hobbyists, 20 
Electronic parts, 362-63 



Electronic projects 

for kids, 21 

loss of appeal, 27 
Electronics 

oonsmiction of;25-26 

hoW>y, 28 

tubes, 26 
Elektor.47 
Elliptic filters, 265 
Engineering 

applications, 200 

students, 9-15 

view by society, 29 
Eiigineering graduates, 10-15 

appiwiticeships, 1 1 

of eleetronics, 10 

professi onai growth path, 11 
Enpiieering graduates, training steps, 12-14 

applications study, 12 

device modelings 1 2^1 3 

first real design, 13-14 

first solo design , 14 

gtaclteig. 14 

layout design, 13 

length, 14 
Engineers 

analog circuit, 35-37 

becoming one, 197-200 

and the growth of analog design, 386 

in Japan, 35-37 

marketing, 200 

next generation of , 37^38 

aaid their wives, 51-54 
Bnt^ainment sysfeern* home, 19 
Epitronics. 301 

Equipment, see also Instruments; Test 

iiistruments 
Equipment 
broken, 5 
repair, 3-7 
Erdi, George, 100 
Experimentation, poor, 59 
Extea^fjast complementary bipolar (XFCB), 
294,315 



Faraday, Michael, 298, 300 
Faraday's Law, 103 
Feedback 

current, 96 

voltage, 94 
Femtofarads defined, 83 
Feynman, Richard R, 55-61, 152 
Field effect transistors (FETs), 70; 72, 75, 
78,81-82, 265 



Filters 

Bessel, 265 

Cauer, 265 

elliptic, 265 

phase linear, 265 
Fixing equipment, 3-7 
Folkes, Martin, 241 
Fourier transform, 35 1, 367 
Frequency and^osciiloscopes, 67-69 
Frequency synthesizersi 350 
Frequency transformations, 35 1-52 
Frequency-dependent-negative resistors 

(FDNRs), 356 
Frequency-Lock-Loops (FLLs), 350 
Frisius, Gemma, 234, 235 
Front-end of instruments, 66 
Fujii, Nobuo, 34 

GaAs MESFETs, 254 
Galley Slave,?>14 
Gelemter, David, 325 
Generators 

function, 367 

sine, 351 

triangle, 351 
Generics, anticipatory, 291 
Gilbert, Barrie, 249, 279-326 
Glometer, 184 
Cod and Golem, Inc,^ 322 
Graduates , engineering, 10-15 
Graham, George, 238 
Grant, Doug, 195, 197-218 
Gridiron pendulum, 238 
Gross, Wilham R, 63, 85-101 
Gross, Winthrop, 135 
Ground plane, 109-11,365 
Grounds, 109-11 



Hallen,Thor, 135, 138 

Halley, Edmund, 238,244 

Ham radio, 18 

Harrison, John, 195, 233-48 

Harrison, William, 242^5, 247, 248 

Harth, Erich. 323 

Harvard Business Review, 300 

Harvey, Barry, 9-15, 17-29 

Heat and vacuum tubes, 19 

Hewlett, BUI, 128 

Hitachi Ltd. research laboratcffy, 34 

Hobbies 

and relationship to careers, 17-29 
and social values, 20 
Hobbyboards, 27, 28 



Hobbyists 

in the '60s, 27 

electronic, 20 
Hodges, Dave, 254, 255 
Home laboratories, 169-11 
Hooke. Robert, 236 
Hubris, 10 

Huygens, Christian, 236 
Hybrids, dual channel, 135-37 
Hypothetico-deduction, 283 

Ideas, creating new, 353-59 
Impedances 

transformations, 351-52 

two-path converters, 76, 77 
Inductive peaking, 122-25 
Inductors, 107-9 
Innovation 

boundary watch, 283 

and computers, 2^6 

creative response, 283 

and effective gatekeepers, 288 

enhancing, 319-20 

and the future, 301-2 

knowledge-driven, 316-19 

and leadership, 303-6 

magnetron, 294 

microwave oven, 294 

in the Nineties, 297-300 

opportunity, imagination, and anticipa- 
tion, 300-301 

personal challenge, 283 

personal side of, 282 

riskiness of, 291 

starts with tomorrow, 283 

and systems theory, 307-10 

things that are too good to be true, 
330-32 

and Thomas Alva Edison, 295-97 
and total quality management (TQM), 

310-12 
wellspring of, 282-87 
Inspiration, 328-30 

clarifying possible solutions, 330 
end-to-beginning technique, 328-30 
and the free floating mind, 328 
random trials, 328 
testing conventional wisdom, 329 
Institute of Electronics, Information and 
Communication Engineers (lEICE) - 
Japan, 31 
Institute of Parapsychology, 61 
Instruments, see also Equipment; Test 
instruments 
front-end of, 66 



knob-driven, 50 

miscellaneous, 21A-11 

repair, 3-7 

of time, 233-48 
Instruments for measurements, 176-83 

probes, 176-79 

RMS voltmeters, 1 79-81 
Integrated circuits (ICs), 85-101 

application specific, 290^91 

data sheets, 100 

design engineers, 85-86 

innovation, 279-82 

linear design, 327-42 

mask designs, 98-99 

new products, 86-87 

testing, 99-100 

user- specific, 290-91 

and vertical amplifiers, 134-35 

and video faders, 87-88 
Intel 8080 microprocessor, 198 
Interstage peaking, 132 
Interviewing by analog applicants, 219-31 

answers to sample questions, 228-30 

the interview, 221-22 

preparation, 219-21 

recommendations, 23 1 

sample questions, 222-27 

technical grilling, 221 

technical interview, 221 
Inventions 

and creativity, 66 

evaluating new ideas, 66 

getting excited about, 66 

giving oneself time for, 65 

mastering the fundamentals, 66 

spirit of, 65--66 

thrives in a multi-disciplinary mind, 286 

Japan, analog circuit engineers in, 35-37 
JFETs, 70, 265, 267 
Johnson noise voltage, 264 

Kendall, Larcum, 246, 247 
Kidd, Dean, 138 
Kids, electronic projects for, 21 
Kirchoff's Law, 103, 109, 112 
Kobbe,John, 129, 134,138 
Koestler, Arthur, 283 
Kovacs, Gregory TA., 41-54 

Laboratories, home 
equipment, 269-77 
cables, connectors, and adaptors, 275 
chart recorders, 274 



diddle boxes, 274-75 
iiiiscellaneous instruments, 274-77 
oscilloscope cameras, 275 
oscilloscopes, 271-73 
picoammeters, 274 
power supplies , 273 
signal sources, 273 
spectrum anal yzefs, 274 
vaiiabie voltage references, 274 
voltmeters, 274 
location of, 275 

and spectacular work gains, 270 
Lamb, Jim, 138 

Lamps, cold cathode fliiorescent, 153, 
154-62 

Laws 

Faraday's, 103 

Kirchors, 103, 109,112 

Lenz's, 103 

Moore's, 249, 251-61 

Murphy's, 99-100, 103, 383 

Ohm's, 103 

of phy sics, 368-69 
Lee, Hae-Seung, 254 
Lenz's Law, 103 

Linear Technology Corporation, 149, 270 
Liquid crystal display (LCD) backlights, 
139^75 

circuil design gamble, 152-53 
circuits, 186-88 

a)ld cathode fluor^cent lamps (CCFLs), 

153 

concluding the project, 174 
current sensing, 1 89-9 1 
development of, 144-46 
and efieiency circuits, 192-93 
efficiency measurements, 164 
examining light bulbs, 143^44 
extending illumination range, 1 71-74 
feedback loop stability, 166-71 
general measurements, 162-63 
layout, 164-66 

looking at established circuits, 145-52 

meaningftil measurements, 176-93 

optimization considerations, 162-63 

power supplies, 186 

st^ng the project, 142-43 

testing ideas, 186 

two-lamp designs, 165-66 
Listening, to customer voices, 290-92 
Lunars , 244 

Lyo^d, Jean-Francois» 285 

MagMtetic fields, 109 

Maiketplace, general knowledge, 279 



Markets 

anticipating future needs, 288 

modeling, 287-90 
Mask designs, 98-99 
Maskelyne, Nevil, 244, 246 
Master-chips, 99 
Matthews, William, 246 
Mayer, Johann Tobias, 243 
Measurements 

calorimetric, 181-83 

electrical efficiency, 181 -83 

instrumentation, 176-83 

photometric, 184-85 

Medawar. EB., 283, 284 

Memory 

comparator, 254-57 

density increase, 251 
MESFETs, GaAs, 254 
Micro-machined relays, 83 
Microprocessors, Intel 8080, 198 
Microsim PSpice Application Design 

ManuaL 338 
Mini-MountSi 115 
MIT (Massachusetts Institute of 

Technology), 3 
Modulation/demodulation, 350 
Mono-chips, 99 
Moon curve, 251 
Moore, Gordon, 251 
Moore's Law, 249, 25 1-61 

analog-to digital converters (ADCs), 
252-53 

brute force vs. elegance, 252-53 
comparator memory, 254-57 
computer circuit simulation, 253-54 
and digital audio, 261 
digital signal processing, 260 
and memory density increase, 25 1 
noise and robustness, 260-61 
sampling the input, 258-59 
successful VLSI architecture, 259 

MOSFETs, 70, 72, 74, 77-78, 254^59 

Moulton, Cliff, 129, 131, 138 

Mudge, Thomas, 246 

Multipliers, analog, 291 

Murkland, Judd, 101 

Murphy's Law, 99-100, 103, 383 

Nagata, Minoru, 34 

National Accelerator Laboratory, 60 

National Semiconductor, 115, 330 

Negative resistance characteristics, 156 

Nelson, Carl, 249, 327-42 

Neural network techniques, 281 

Nguyen, Dung (Zoom), 101 



Norton equivalents, 351-52 
Nuclear magnetic imaging (NMI), 305 
Nuclear magnetic resonance (NMR) tech- 
niques, 305, 306 

Ohm's Law, 103 

Olson, Oscar, 138 

Olson, Ron, 138 

Open loop linearity, 95 

Orbit Semiconductor, 255 

Oscilloscope cameras, 275 

Oscilloscopes, 271-273, see ato Tektronix 
distributed amplifiers in, 128-29 
frequency and time domains, 67-69 
high impedance at high frequency, 69-77 
and impedance converters, 69-77 
signal conditioning in, 65-84 
T-coils, 121-38 

Palmer, William, 237 

Parasitics, 70-72 

Parts, electronic, 362-63 

Patent specification, 128 

Pease, Robert A., 115, 33 1 , 363 

Percival,W.S., 128 

Phase compensation, 134 

Phase linear filters, 265 

Phase-lock-loops (PLLs), 350 

Philosophy of design, 330-42 

Photometric measurements, 1 84-85 

Pi, 388, 389 

Picoammeters, 274 

Pietkiewicz, Steve, 270 

PIN diodes defined, 82 

Plank, Stephen, 237 

Plessey Research Labs, 281 

Polits, Bill, 129 

Popular Electronics, 41 

Powder of sympathy, 233 

Power supplies, 273 

Practical Wireless, 281 

Probes, 176-79 

Product development, 201-7 
finding customers ,213-16 
finding a solvable problem, 201-6 
moving on to the next problem, 216-17 
problems worth solving, 206-9 
project design and construction, 209-13 
speaking the customer's language, 204 

Product innovation 

algorithmic approaches, 279 
anticipation, 279 
significantly different, 279 



Products 

mature generic, 290-92 

new, 86-87 
Proportional to absolute temperature 

(PTATs) sensors, 330 
Pseudo-noise (PN), 350 
Pseudo-random noise (PRN), 350 

Radios 

ham, 18 

transistor, 22 
Radios, AM, 17, 18 
Rag chewers, 18 
Reay, Robert, 195, 219-31 
Relays 

double-pole double-throw, 79 

micro-machined, 83 

single-pole single-throw, 79 
Repairing equipment, 3-7 
Resistances, 104-5 

negative characteristics, 156 

temperature-coefficients of, 3 1 5 
Resistors, Frequency-dependent-negative, 
356 

Rhiger, Richard, 128, 138 
RMS voltmeters, 179-81 

Ruke8920A, 180 
Hewlett-Packard HP3400A, 181 
Hewlett-Packard HP3403C, 180 

Roach, Steve, 63, 65-84 

Rocky Mountain Inventors' Congress, 65 

Ross, Robert, 135, 138 

Royer converters, 148-49, 158, 167, 168, 
173 

Royer, George H., 148 

S.O. (significant other), 48, 52, 53 
Santa Cruz, Alonso de, 235 
Saunderson, Nicholas, 237 
Science, cargo cult, 55-61 
Scientific integrity, 58, 61 
Scientists 

not fooling laymen, 58 

not fooling selves, 58 
Scopes ; see Oscilloscopes 
Sekine,Keitaro, 31-39 
Sellum, Yucan, 295, 296, 298 
Sensors, proportional to absolute tempera- 
ture, 330 
Shop (Renaissance concept), 1 1 
Signal conditioning in oscilloscopes, 65-84 
Signal sources, 273 
Signals Research and Development 
Establishment (SRDE), 28 1 



Significant other (S.O.), 41 
Sitntilations, computer. 253-54 

Sine generators, 351 

Single-pole single-throw (SPST) relays, 79, 
80 

Skiiicffect, 104, 105 

Soak times, 256 

Social values, and hobbies, 20 

Solder-Mounts, 115, 116 

Solomon, Jioi, 288 

Source followers, 70, 72, 73, 77 

Sousae, Jim, 101 

Spectrum analyzers, 274, 367 

SPICE 38, 45, 93, 13B, 255, 317 

Spottsc alignment imit(SAU), 53-54 

Staia, Ray, 281,320 

Statistical theory of communication, 286 

Step recovery diodes, 267 

Step responses and oscilloscopes, 68 

Sdifi^ pitnering, 

Stray capacitances, 105, 106, 132 

Siudjenis, engineering, 9-15 

Super capacitors, 356 

Super diodes, 93 

SUperccmductor assumptions, 109 

Suttler, Goodloe, 320 

Swanson, Eric, 249, 251-61 

Switching regulators, Linear Technology 

LT1172,149 
Sylvama, wotidng at, 122 
Synlhesixers, frequency, 350 
Systems theory, 307-10 

T-coils 

and dual channel hybrids, 135-37 

with IC vertical amplifiers, 1 35 

in oscilloscopes, 1 21-38 

peaJiiiig capacitance loads, 125 

and pliase compensation, 134 

responses, 125-28 

and stray capacitance, 132 

theoretical and practical proportions, 
\ih32 

in transistor interstages, 133 
T-coiJ s, inductive peaking, 1 22-25 

charging of capacitances, 1 22-23 

resistors and charging of capacitors, 124-25 
Tfechnical grilling, 22 1 
Technical interviewing, 22 1 
Tektronix 

1A7 oscilloscope, 4 

3 A6 oscilloscope, 125 

454A portable oscilloscope, 6 

Sii) series oscilloscopes, 129 

7000-sertei oscilloscopes, 281 



7904A oscilloscopes, 50 

CRT circuits, 149 

J-17/J1803 photometers, 184 

oscilloscope design, 281 

working at, 122 
Tektronix Integrated Circuits Group, 

134-35 
Temperature chamber, 367 
Temperature-coefficient of resistance 

(TCR),315 
Tesla, Nikola, 279, 299, 300 
Test instruments, see also Instruments 

comments, 49-51 

Tektronix, 50 
Thermometer effect, 1 7 1 , 1 72 
Thermometering, 172, 173 
Thevenin equivalents, 351-52, 353 
Thought processes, 6 
Time domains and oscilloscopes, 67-69 
Time, father of atomic, 3 
Time instruments, 233-^8 
Tokyo Institute of Technology, 34 
Tone detectors, 350 

Total quality management (TQM), 310-12 
Transistor interstages, 133 
Transistor radios, 22 
Transistors 

and circuit design changes, 24-25 

circuits, 26 

commercial, 23-24 
Translinear principles, 281 
TRF receivers, 280 
Triangle generators, 351 
Troubleshooting, 363-71 

common mistakes in, 363-64 

dealing with ground, 365 

disproving laws of physics, 368-69 

evaluating the design, 374 

failure analysis, 370-71 

having clean circuit boards, 365-66 

having proper test equipment, 366-68 

making approximations, 364-65 

making assumptions, 364 

testing the equipment, 371-74 

and true failures, 369-70 
TTL gates, 198 
Tubes, vacuum, 19, 26 
2001: A Space Odyssey, 324 

User-specific integrated circuits (USICs), 
290-91 



Vacuum tubes, 19, 26 
VAX-780, 292 



Vertical amplifiers, 135 
Video faders 

circuits, 89-94 

and current feedback, 96 

redefinition, 94-98 

and voltage feedback, 94 
VLSI circuits, 252, 253-54 
Voice of the customer (VOC), 203, 208, 

282. 294, 296, 306-7 
Vollum, Howard, 128, 320 
Voltage 

compensated divider, 77 

feedback, 94 

Johnson noise, 264 

transfer ratio, 352 
Voltineters, 274 



Wager, Sir Charles, 239 
Wainwright, Claire R., 1 15 
Wainwright Solder-Mount System, 1 15, 
116 



Wein bridge, 353 

Welland, Dave, 254, 258 

Whiston, William, 233,234 

Whit^urst,ToddK.,41 

Wideband amplifiers, 137-38 

Widlar, Bob, 288, 289, 329 

Wiener, Norbert, 286, 322 

WiUiams, Jim, 3-7, 41, ^3, 139-93, 249, 

269-77 
Willison, John, 249, 263-67 
Wilson, George, 134, 135 
Winn, Sir Rowland, 237 
Wireless World A1 
WMM GmbH. 115 

Young, Steve, 140 
Yours is the Market, 295 

Zacharias, Jerrold R., 3